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The development of high yielding cultivars with better quality and longer shelf life in strawberry has been a long-term research objective. Selection of cultivars having improved fruit quality with higher post harvest shelf life and proper handling is prerequisite for successful cultivation in strawberry crop (Huang and Yang, 2003).
Maximum crown size was found in cv. Tuft followed by cvs. Pocahontas and Cruz. This observation is in agreement with studies conducted by Camacaro et al., (2002) who reported differences in growth and yield in the June-bearing strawberry (Fragaria ananassa) Elsanta and the day neutral cultivars Bolero and Everest. Growth, development and yield showed considerable differences among cultivars. Elsanta showed the highest and Bolero and Everest exhibited the lowest values for almost all the vegetative parameters (leaf area, leaf dry weight, runner number). Elsanta produced larger leaves and few crowns per plant in contrast to the ever bearing cultivars, which had greater number of smaller leaves and a larger number of crowns per plant. Kaska et.al., (1997) reported that the H-1, Selva, Tufts and Elsanta appeared to be vigorous, and Chandler, Addie, Redchief, Lester and Honeoye have weaker vegetative growth in Turkey. During the present investigation, variations in the leaf area index and crown size might be due to differences in their genotypic make up. Previous studies have shown genotypic variability in solanaceous vegetables for vegetative growth (Rao and Bhatt, 1991., Pillay et al., 1990). The plant height has been reported to be possibly affected by environmental conditions (Kreidemann 1986; Barlow et al., 1980) and management practices (Turemis et al., 1996).
The fruit yield in strawberry has been found to be positively correlated with the root and runner biomass per plant (Dradi et.al, 1997). The cv. Chandler exhibited maximum shoot and root dry weights. The cv. Tioga and Elsanta produced lower shoot dry weight as compared to the rest of the cultivars. Whereas, cv. Elsanta showed higher root / shoot ratio followed by cv. Tioga.
The accumulation of greater biomass by the cv. Chandler might be due to higher leaf area index (LAI) which possessed positive and significant correlation (r=0.473**) with chlorophyll content, might have contributed to higher rate of photosynthesis. Camacaro et al., (2002) studied the seasonal patterns of radiation use efficiency and assimilate partitioning and concluded that growth, development and yield showed considerable differences among cultivars.
Higher root / shoot ratio with lower shoot and root dry weight in cv. Elsanta indicates relatively greater movement of assimilate to roots which might be at the expense of leaf production. Whereas, in case of cv. Chandler better shoot growth was also associated with greater root growth, which allowed exploiting a larger soil volume for water and nutrients as previously reported by Amberger, (2006).
The cv. Elsanta exhibited higher roots/ shoot ratio. The root / shoot ratio is a good indicator of the plant's tendency to partition assimilates preferentially to the roots, rather than the leaves. However, higher root / shoot ratio is not necessarily a useful criterion for higher yields, because; the genotypes having higher root / shoot ratios partitioned relatively greater proportion of assimilates into roots at the expense of leaf production (Mahmood, 1999). The dry root weight exhibited positive and significant correlation (r=0.628**) with root / shoot ratio.
Maximum photosynthesis is positively related with green leaf N content (Field and Mooney 1986). Similarly, the nutrient status of plants has been reported to significantly affect the fruit quality in strawberry (Kirnak et al., 2001).
The cv. Chandler showed maximum leaf N, P and K contents followed by cv. Cruz for N cvs. Tioga and Elsanta for P and cvs. Cruz and Tuft for leaf K respectively. Previously Miquelao et al., (1994) found difference in response of strawberry cultivars Chandler and Guarani to the fertilizer treatment. Chen and Lenz, (1997) reported that total plant dry matter increased with sufficient P content as compared with ambient CO2 and deficient P. The P deficiency decreased concentrations of N, K, Mg and soluble carbohydrates, and increased root / shoot ratio and starch concentration in roots, stems, runners and leaves at both ambient and doubled CO2. During the present research work, a synergistic relation was found between leaf N and P content. Similar results have been reported earlier by Bethlenflavay (1991).
Chlorophyll plays important role in the photosynthetic machinery of plants which is closely related (r=0.616** for dry shoot & r=540** for dry root) with biomass production.
The cv. Chandler has shown maximum chlorophyll content followed by cvs. Pocahontas and Elsanta. Chlorophyll contents of all cultivars were decreased in 2006 which might be due to variations in environmental conditions i.e., less leaf area in all the cultivars due to decrease in average minimum temperature (3.75oC) and increase in average maximum temperature (1.55oC) as compared to the year 2005. In addition to this, low rain fall also decreased LAI hence contributing towards decreased chlorophyll contents in all cultivars (Table 1). These results are in agreement with findings of Dradi et.al., (1997) who found that the cultivar 'Chandler' with higher LAI, promoted the solar radiation intercepted by the canopy thus increasing leaf chlorophyll contents. Yang et al., (2001) reported that decrease in chlorophyll contents of the leaves might be attributed to the increased rate of chlorophyll degradation as compared to decreased rate of biosynthesis.
Maximum single fruit weight and length was exhibited by the cvs. Chandler, Tiogo and Tuft respectively in both years because of positive significant correlation (r=0.450**) of single fruit weight with fruit length. Verma et.al., (2002) also reported that the fruit volume was significantly correlated with the single fruit weight and number of fruits per plant was positively correlated with fruit length, fruit width, and fruit volume. The cv. Cruz possessed single fruit weight which was minimum as compared to the other cultivars. The number of fruits per plant, single fruit weight and fruit volume are good criteria for selection in strawberry (Verma et.al. 2002), Ozdemir et.al., (2001) who reported that Pajaro, Camarosa and Sweet Charlie were best in terms of single fruit weight and quality. Maximum fruit yield was recorded in cv. Chandler during both the years. The fruit yield of cv. Chandler was followed by Pochantus for fruit weight ant fruit length. The increase or decrease in leaf area has its positive or negative impact on fruit size and yield respectively. The difference among strawberry cultivars for fruit weight has also been reported by several workers (Ozdemir et.al., 2001; Ozdemir, 2003; Yommi et.al., 2003 and Nuzzi et.al., 2005. The higher yields of Bolero and Everest also reflected the greater number of crowns produced by these cultivars. (Camacaro et.al., 2002). The highest yields were obtained from Tufts, and the lowest yields were obtained from Aliso (Turemis et.al., 1996). Chandler et al., (2002) found that there was a significant, but low, correlation between plant vigor and early season yield.
The balance between sugars and acids, which define sweetness and tartness of fruits, give the characteristic flavor of strawberries, while aroma is derived by the combination of volatile molecules (Ayala-Zavala et al., 2004).
During present investigation, it was found that the acidity was markedly higher in cv. Elsanta closely followed by cvs. Pocahuntas, Tioga, and Cruz respectively. Minimum acidity was found in cvs. Aliso and Tuft in both the years.
The cv. Chandler showed higher pH of fruit followed by cv. Tioga whereas cultivars Tuft and Pocahuntas attained minimum pH. Difference among strawberry cultivars for acidity, TSS and pH of fruit has been reported by several workers (Yommi et.al. 2003 and Nuzzi et.al., 2005).
Ozdemir et.al., (2001) reported that strawberry cultivars Pajaro, Camarosa and Sweet Charlie were best in terms of fruit weight and quality.
According to ascorbic acid contents and fruit firmness, no marked differences were observed among the selected strawberry cultivars 24hrs after storage at ambient temperature. These characteristics of the selected cultivars might be due to the reason that the firmness is affected by the cultivar type, its nutrional status and type of fertilizers used (Mukkun et al., 2001). There was found significant and positive correlation (r=0.434**) between acidity and ascorbic acid content.
Straw berry is one of the most perishable fruits with short shelf life due to the susceptibility of berries to mechanical injury, water loss, decay and physiological deterioration (Nunes et al., 1995). Cultivar Chandler and Tuft exhibited minimum losses in fruit weight and fruit spoilage, whereas Pocahontas, Aliso, Tioga, Elisanta and Cruz showed higher values for these parameters after 24 hours storage at ambient temperature. Maximum shelf life (3 days) were found in Chandler and Tuft followed by Elisanta = Tioga = Aliso = Pochantus > Cruz respectively. The TSS was positively and significantly correlated (r=0.536**) with ascorbic acid and fruit weight.
Much research has been conducted and there were efforts of manipulating preharvest (Mukkun et al., 2001) and post harvest factors (Cordenunsi et al., 2005) that affect fruit quality in order to enhance strawberry shelf life.
From the above discussion, it can be inferred that cvs. Chandler and Tuft exhibited higher shelf life, lower pH and TSS value and therefore, could be potential cultivars for production of good quality strawberry.
Experiment No 2
4.2 Response of strawberry cultivar chandler to different mulching materials.
The present investigation was undertaken to determine the response of strawberry cultivar 'Chandler' to different mulching materials such as wheat straw, rice straw, transparent plastic and black plastic mulch. Strawberry plants were grown in open field conditions using different mulching materials as preharvest treatments.
Mulching is the most important agricultural practice in strawberry crop being exercised world over. In addition to moisture conservation and temperature regulation, it avoids the contact of berries with soil and thus minimizes the chances of fruit rot, which adversely affects post harvest life of the berries. Use of proper mulch is, thus, equally important for increasing shelf life (Sharma, 2002)
During present investigation, it was found that all mulched plots maintained higher soil moisture content at 30 cm depth for a longer period of time. Among the mulches used, black plastic mulch had higher average soil moisture content followed by rice straw mulch and wheat straw mulch respectively.
Moisture conservation by mulching has been reported by many authors including Mahrer et al., (1984), Streck et al., (1994), and Streck et al., (1996a). This occurs due to the fact that in the mulched soil the evaporating soil moisture condenses on the insulating substances and drips down again to the soil surface. On the other hand, the water loss from control is very intense and appears to be the function of net radiation arriving the soil surface as observed by Hesse, (1985).
The results obtained during the present investigation revealed that soil moisture was maximum (39.08%) in the black plastic mulch while minimum (30.61%) in control. Improvement of water infiltration and higher water retention resulting from applications of organic materials and mulches has also been reported by Swenson and Chong, (2004), Miller et al. (2002), Arriaga and Lowery (2003) and Hedau et al., 2002). It can be inferred that application of black plastic mulch and rice straw mulch could be highly effective in maintaining soil moisture content in strawberry fields.
Black plastic mulch treatment retained maximum (22.3oC) soil temperature followed by transparent plastic mulch (21.37oC). The potential of organic mulches (wheat and rice straw mulch) to retain soil temperature was lower than black plastic mulch.
Similar increase in soil temperature under black plastic mulch has been reported previously by Diaz et al., (2004). Minimum soil temperature under rice straw mulch indicated effectiveness of organic material as insulating material creating a conducive environment. Similar findings have also been reported by Schonbeck and Evanylo (1998) that organic mulches reduced afternoon soil temperature and maintained higher soil moisture levels. Agele et al., (1999) reported that mulching reduced soil temperature at 5 cm depth and conserved soil moisture at 10 cm depth. The temperature difference was 9oC higher in black plastic mulch than rice straw mulch. These results are in agreement with those of Diaz et al., (2004) who found that mean soil temperature under black mulch was 9°C higher than that under organic mulch.
Mulching improved plant growth and development. Rice straw mulch produced the tallest plants. Minimum plant height, leaf area index and crown size was recorded in control plants. The highest leaf area index and crown size was recorded in black plastic mulch followed by rice straw mulch. Root length was markedly higher in rice straw mulch and transparent mulch followed by wheat straw mulch. Increase in growth characteristics by mulching and organic matter application have also been reported by Agele et al., (2000) and Balraj et al., (2005). Effect of mulch and organic application on improvement of root development and rate of water and mineral uptake in strawberry has been reported by Dobbelaere (2000). The use of green manure or other crop residues for corn (Pallant et al., 1997 and Nickel et al., 2005) and organic amendments for potato (Opena and Porter, 1999) appeared to increase crop root length density. The present investigation established the fact that mulching improves the vegetative growth in strawberry. Similar results have been reported by Moor et al. (2004).
The soil moisture was positively and significantly correlated with soil temperature (r=0.808**), single fruit weight (r=0.446*), plant height (r=0.586**), root length (r=0.586**), crown size (r=0.59**), leaf area index (0.654**), chlorophyll content (r=0.606**) and fruit weight (r=0.881**). Similarly, the correlation between plant height and root length was significant and positive (r=0.786**).
Mulching increased the leaf chlorophyll content as recorded in black plastic mulch and rice straw mulch followed by wheat straw mulch. This could be due to the fact that mulching also improved the leaf area index (LAI). The increased vegetative growth and leaf area index (LAI) promote the solar radiation intercepted by the canopy and thus increase leaf chlorophyll contents as stated earlier by Kirnak et al., (2001).
The leaf area index was significantly and positively correlated with chlorophyll content (r=0.721**) and fruit weight (r=0.712**). The leaf chlorophyll content showed positive correlation with crown size (r=0.594**)
Black plastic, transparent plastic and rice straw mulches produced maximum single fruit weight. However, the highest fruit length was found in wheat straw mulch followed by black plastic mulch. Whereas, maximum fruit width was recorded in rice straw mulch. It was observed that mulching influenced yield significantly in strawberry , maximum yield (210.0 g) was obtained by the use of black plastic mulch followed by wheat (201.8g) and rice straw (187.8g) mulch. Similar studies have been reported by (Kaska et al., 1988; Moor et al., 2004) they concluded that mulches had significant influence on yield and quality of strawberry.
The ascorbic acid content in fruits and vegetables is an important ingredient (Lee and Kader, 2000).Mulching treatments have significant effect on ascorbic acid contents of strawberry crop. Ascorbic acid contents were lesser in black plastic mulch treatment as compared to bare ground treatment. This is in line with studies conducted by (Klein and Perry, 1982, Lee and Kader, 2000). They stated that the temperature is the most important factor in determining the ascorbic acid content of the commodity. The relatively low content of ascorbic acid could be the causes of high temperature during ripening of the fruit.Total soluble solids (TSS) were considerably affected by the mulching treatments. Black plastic mulch treatment showed higher TSS closely followed by transparent plastic mulch and rice straw mulch as compared to the rest of the treatments. Moor et al., (2004) documented the cause of high content of TSS could be the high light intensity during fruit development and ripening..
Organic mulching (wheat and rice straw mulch) reduced weight loss and fruit spoilage in strawberry fruits and improved the shelf life. Minimum fruit spoilage and weight loss was recorded in wheat straw mulch and rice straw mulch respectively. The black and transparent plastic mulch increased the weight loss in strawberry cultivar 'Chandler'. The increase in weight loss in strawberry fruit produced under plastic mulches could be due to high soil temperature which affects the growth inhibitory hormone and ethylene stress might be increased under high soil temperature produced by these mulches.
The fruit shelf life was positively and significantly correlated with fruit weight (r=0.627**). Similarly, the correlation between TSS and single fruit weight was positive and significant (r=0.61**). Whereas, the single fruit weight was positively correlated with fruit weight (r=0.59**).
Our results are in confirmatory with the findings of Diaz et al., (2004) and Schonbeck and Evanylo, (1998) who reported that the growth and productivity is positively influenced by black plastic mulch. Others workers have reported similar effects of mulches and organic application on fruit yield of tomato (Villareal, 1980; Agele et. al., 1999; Hudu et al., 2002 and Sharma and Agrawal, 2004). Black plastic mulch have been reported to have lower yield due to high root zone temperature, which has been shown to interface with the reproductive development in numerous species, including tulip, iris, chrysanthemum, pepper and strawberry (Willits and Peet,1998; Anderson, 2002). Schonbeck and Evanylo, (1998) reported that mulch treatments apparently affected early, strawberry yield by influencing soil temperature regime but affected yields by modifying soil moisture levels . Similar results have been reported by Agele et al., (2000) that the grass mulch ameliorated the hydro-thermal regime of the soil, improved the vegetative growth and flowering and significantly increased the fruit yield of strawberry over bare ground. Moor et al. (2004) have described that application of organic mulch is better than plastic mulch as for as quality of strawberry is concerned.
Experiment No 3
4.3 Effect of gibberellic acid (GA3) on growth, yield, quality and shelf life of strawberry cv. Chandler
Four concentration of GA3 (50, 75, 100 and 150ppm) were evaluated for various growth and quality parameters under similar field conditions during 2006 and 2007.
Application of gibberellic acid (GA3) is a common agricultural practice to break flower bud dormancy. This treatment extends the strawberry growing season thereby increasing fruit yield (Ozgüven and Yilmaz, 2002).
Exogenous application of (GA3) at all growth stages improved the endogenous GA level in cv. Chandler. The endogenous gibberellins (GAs) play a dogmatic role in stem elongation and flowering of some cold-requiring plants (Hasebroek et al., 1993., Zanewich and Rood, 1995) by increasing endogenous gibberellic acid level (Pharis and King, 1985). Similarly, He et al., (2009) reported that exogenously applied GA3 significantly increased the endogenous level of gibberellic acid in red globe growth.
The exogenous application of GA3 improved plant height, leaf area index (LAI) and crown size in cv. Chandler. . Different marked differences were found among the treatments which may be due to induction of endogenous GA3 level which in turn increase growth and biomass of the plant e.g. maximum shoot and root dry weight was observed in plant treated with 75ppm.
GA3 has been reported to improve vegetative growth in short day strawberry cultivars cultivated under non-inductive conditions for flowering (Braun and Kender, 1985., Franciosi et al., 1980). Similarly, Hisamatsu et al., (1998) reported that exogenous application of GA3 increased stem elongation in Matthiola incarta which contributed to the plant height. Jaleel et al., (2009) found that exogenously applied GA3 positively influenced the plant growth in Catharanthus roseus. Gibberellins play integral role in plant development processes and enhance a number of enviable effects including stem elongation, uniform flowering, reduced time to flowering and increased flower number and size (Jaleel et al., 2009). GA3 stimulates cell elongation in plants (Jaleel et al., 2009) which might have resulted with the maximum plant height in strawberry cultivar 'Chandler' during present study.
The GA3 treated plants showed higher concentration of leaf nitrogen and phosphorus. The GA3 at 150 ppm was more effective.
Significant interactions were found between endogenous GA3 content and N content for dry weight of leaf, fresh and dry weight of root, and leaf thickness but not for leaf area or stem growth (fresh weight, dry weight, height) in brussels sprout (Selman and Bora 2008). This study indicated that GA3 play prominent role in increasing the N content of plants. The exogenous application of GA3 increased the mineral nutrient levels of Vigna unguiculata roots and shoots (Al-Rumaih (2003). In addition, many studies have revealed the regulatory role of GA3 in selective ion uptake and allocation in plants through their effect on membrane properties and effect transport of various substances, including assimilates (Steveninck and Van 1976). The GA3 improved the nutrient status of strawberry cultivar Chandler.
The GA3 has been reported to improve yield and fruit quality of strawberry. During present investigation, it was found that the exogenously applied GA was highly effective in increasing the fruit size, width and fruit length. This increase in yield can be attributed to the increase in cell size.
The leaf area index showed positive and significant correlation with crown size (r=0.876**), chlorophyll content (r=0.801**), plant height (r=0.806**) and fruit weight (r=0.747**).
The beneficial effects of GA3 on plants regarding yield include shortening of the time from planting to first harvest, increase of early yield, total yield, number of fruits, and duration of harvest period (Tehranifar and Battey, 1997). Sharma and Singh, (2009) indicated that GA3 (75 ppm) spray either during mid-November or mid-February or at both times has favorably influenced all vegetative attributes and yield parameters of strawberry over control. Benjawan et al., (2006) reported higher fruit yield in mango when GA3 was applied as foliar spray during flowering. Exogenous treatments of GA3 improved weight, size and color of strawberry fruits (Montero et al., 1999).
After 48h of GA3 application, the endogenous GA3 exhibited positive and significant correlation leaf area index (0.889**), crown size (r=0.878**), chlorophyll content (0.779**), plant height (r=0.859**) and fruit weight (r=0.922**). Similarly, the fruit weight showed positive and significant correlation with plant height (r=0.871**). After 96h of exogenous GA3 application, the correlation between endogenous GA3 and single fruit was positive and significant (r=0.876**).
The GA3 was highly effective in increasing the ascorbic acid content of fruits. However, maximum ascorbic acid content was recorded in fruits collected from plants treated with 75 ppm GA. The foliar application of GA3 was ineffective in altering the acidity of fruits. The total soluble solids (TSS) level was markedly increased by exogenously applied GA3. Although interaction of treatments and year were highly significant regarding pH of fruit however there was no consistency among treatments in both years. The quality parameters of strawberry like TSS and ascorbic acid contents have been reported to be positively correlated with exogenous application of GA3 (Sharma and Singh 2009).
Shelf life is an important determinant of storage capability of fruits. Improved shelf life increases the marketability of fruits particularly in strawberry having short shelf life.
The exogenously applied GA3 decreased the shelf life of strawberry. Minimum shelf life of fruits was recorded in plants treated with higher concentrations of GA. Marked increase in spoilage of fruits was recorded when straw berry plants were treated with higher concentrations of GA3. These results are contradictory with previous findings which showed that preharvest foliar spray of strawberry crop with GA3 improved the shelf life of fruits (Asrey 2003). The fruit firmness was not affected by exogenous application of GA3 in strawberry cultivar Chandler during present investigation. McLaren and King, (1989) while working with cherry reported that fruit firmness was not affected by GA3 application. It can be deduced that application of GA3 could be highly effective in improving growth, fruit yield and quality in strawberry cultivar Chandler. Further more, application of GA3 could be a substitute of chilling treatment. Tehranifar, A. and Battey, N.H. 1997. compared effects of GA3 with chilling and stated that GA3 causes an increase in vegetative growth which is similar to the effect of 4-6 weeks chilling.
Experiment No. 4
4.4 Performance of strawberry cultivar Chandler under different environmental conditions
The aim of the present investigation was to determine the performance of strawberry cultivar 'Chandler' at varying chilling temperatures subjected to different environmental conditions. The plants were initially chilled at different temperatures of 30C, 50C and 70C for two weeks and then transplanted to open field, poly tunnel and shade house simulating three environments. The data were recorded on the following morphological, physiological, yield and qualitative attributes.
Strawberry plants can be grown under mild winter climates for off season production. In these circumstances better production may be obtained by specific treatments, depending on the cultivar and the environmental conditions (Lieten, 1991. F. Lieten , Greenhouse strawberry culture in peat bags. Adv. Strawberry Prod. 10 (1991), pp. 56-57.Lieten, 1991). The optimum temperature required for growth of strawberry ranges from 100C to 260C that is why it grows better in temperate climates (Strik, 1985). Therefore, during present investigation, the effects of different temperature regimes on growth and yield were compared on good performing strawberry cultivar 'Chandler' under varying environmental conditions. The plants achieved maximum height and leaf area index when chilled at 30C and grown in polytunnels (Table ). Under open conditions, plants chilled at 30C produced maximum number of leaves (Table). The plants which were given the chilling temperature at 70C and grown in poly tunnel exhibited maximum crown size (Table), while maximum root length was observed for plants given chilled at 70C and grown in shade house.
Different studies reveal the effect of environmental factors on growth and productivity of strawberry. It has been documented that at the end of summer, reduction in vegetative growth is photoperiod and temperature dependant (Heide, 1977; Durner et al., 1984). During the present study, it was found that chilling of runner at 3C and growing of plants in poly tunnel exhibited higher plant height and leaf area index which might be due to the availability of warmer environment inside the poly tunnels. Low temperature decreases the stem elongation compared to a high day/low night temperature combination. The temperature regimes stimulate growth elongation which is accompanied by an enhanced level of GA1, GA19, and GA44 (Jensen et al. 1996).
The plant height was positively and significantly correlated with single fruit weight (r=0.673**), crown size (r=0.64**), endogenous GA3 content (r=0.591**), chlorophyll content (r=0.775**), leaf area index (r=0.655**) and fruit weight (r=0.64**). Similarly, the correlation between single fruit weight and endogenous GA3 content was also positive and highly significant (r=0.802).
During present findings, the chilling treatment of runners at low temperature (30C) and their growing in polytunnels stimulated the plant height, number of leaves and leaf area index in strawberry cultivar 'Chandler'. Therefore, it can be inferred that chilling at 30C could be highly effective for achieving maximum vegetative growth in strawberry. Moreover, the polytunnels can provide optimum growth conditions for better growth which might be beneficial for strawberry growers during cold seasons. The results further established that chilling could be a better option in breaking dormancy of strawberry runners when the natural environmental conditions are not favourable. These findings are in line with the findings of Hamano (2009).
The chilling treatment of runners at different temperatures did not affect the chlorophyll content in strawberry. However, the environmental conditions markedly increased the chlorophyll content, maximum being in plants grown under polytunnels. The increase in chlorophyll content of plants growing in polytunnels might be due to warmer environment inside the polytunnels. The chilling treatment of runners at 70C greatly increased the endogenous GA3 content in plants grown in polytunnels. The polytunnels has been reported to increase the soil temperature and enhance productivity (Sarooshi 1982). Pinthus (1989) while working on wheat found that endogenous content of GA was closely related with temperature and was three fold higher at 25°C than at 10°C. The correlation between chlorophyll content and endogenous GA3 content was positive and significant (r=0.795**). During the present investigation it was found that polytunnels resulted in higher chlorophyll content which might be due to higher endogenous GA3 as was recorded during present investigation. Wheeler and Humphries (1963) have reported that GA was highly effective in increasing the chlorophyll content per leaf in potato. Similar observations were also reported by Kim et al. (2004) that GA increased the leaf area and chlorophyll content in the peaches.
Environmental conditions controlling the transition from vegetative to floral growth are playing a dominant role in the production of strawberry. The plants raised from runners chilled at 30C and grown in polytunnels exhibited maximum single fruit weight and fruit weight per plant. However, fruit size was not affected by all the chilling treatments.
These results are in agreement with previous findings of Palencia et al. (2009) who reported that strawberry production could be affected by climatic conditions. They found that there was linear relationship between the rate of production and temperature but at higher temperatures, the fruit yield was significantly decreased. The polytunnels provided optimum environment to the strawberry plants which caused increase in the fruit yield. Jemmali and Boxus (1993) found that more flowers per plant were produced under optimum temperatures in the green house. Similarly, In the strawberry cultivars 'Florence' and 'Korona' yield increased significantly when night temperature increased from 9 to 18 °C, while the optimum temperature for cultivar 'Frida' was 15 °C that was grown under cool-environment conditions Sønsteby and Heide (2008). Miura et al. (1994) have reported that fruit size in strawberry is not dependant on number of fruits per plant, but it is dependant on the intensity of growing temperature. According to Larson (2004), plastic mulch resulted in higher yields in strawberry and concluded that irradiation and temperature are the most important factors which determine fruit yield and quality in strawberry. It can be concluded that polytunnel could provide optimum environmental conditions for better growth of strawberry during cold weathers.
There was found positive and significant correlation (r=0.745**) between fruit weight and endogenous GA3 content. Similarly, the fruit weight was also positively and significantly correlated with single fruit weight (r=0.857**), crown size (r=0.629**), shelf life (0.505**), chlorophyll content (0.749**) and leaf area index (r=0.758**). The correlation between shelf life and endogenous GA3 content was positive and significant (r=0.257*).
During the present investigation it was found that TSS content was not affected either by chilling treatments or environmental conditions. The plants grown in open field conditions possessed minimum loss in fruit weight. Previous findings revealed that higher temperatures caused weight losses in strawberry. According to Miura et al. (1994), high temperature (190C) was closely related with weight loss in strawberry cultivar Toyonoka. Asami et al. (2003) have found that in strawberries grown under sustainable conditions, the ascorbic acid content was higher than in conventionally-grown fruit. The TSS was significantly and positively correlated (r=0.282*) with fruit length.
From the above discussion it can be concluded that chilling treatment of runners at 30C and growing of strawberry cultivar Chandler in poly tunnel, could produce greater yields and good quality fruits.
Experiment No. 5
5.5 Effect of different storage temperatures, packaging materials and chemical treatments on the shelf life of strawberry
The aim of the investigation was to determine the impact of different storage temperatures [room temperature (20± 30C) and 4 0C)], packaging materials (cardboard boxes and polythene bags) and chemical treatments (calcium chloride at 0.5, 1 and 1.5%) on the shelf life of strawberry cultivar Chandler.
The storage temperature is a prime factor that has a definite impact on shelf life of strawberry fruits. In the market, strawberries are usually kept at room temperature ranging from 18-20 0C (Gracia et al. 1995. Perez et al. 1999). Furthermore, modified atmosphere along with special packaging and chemical treatments have been tested to improve shelf life of strawberry (Sanz et al. 1999., Morris et al. 1985). Calcium is a divalent cation that enters the apoplast and is bound in transferable form to cell wall and peripheral surface of plasma membrane. Concerning the exploitation of calcium during post harvest studies of fruits showed that it conserves their quality, preserve physiological disorder, reduces the rate of respiration and slow down the ripening process in apple, tomato and peaches (Burns-e- Pressey 1987).
There was found reduction in weight loss with prolongation of storage period. However, the treatment of strawberry fruits with calcium chloride ameliorated the weight loss and improved the storage stability. Calcium is the important mineral constituent and it is the constituent of middle lamellae. Softening of fruits is largely due to weakening of middle lamellae during ripening. Calcium helps in binding of polygalactonic acid each other and make the membrane strong and firm. Calcium had been commercially applied in apple to increase the shelf life and reduce the post harvest disorders (Sharma et al 1996). During present investigation, the improvement in shelf life by calcium application might be due to delay in senescence, rate of respiration and transpiration in strawberry fruits. Minimum physiological weight loss was observed in 1% calcium chloride treated fruits which matched with the results of Bhattarai and Gautam (2006). The storage of fruits at 40C maintained higher shelf life. Similar results were found by Hagg et al. (1999) that lower temperatures (2-5 0C) extended shelf life in strawberry fruits.
It was evident that highest firmness was observed after 13 days in fruits treated with 1% calcium chloride and kept at 4 0C in card board boxes. Shin et al, (2007) found the same result during their research on post harvest keeping quality of strawberries. They described that one of the most important factors to modify the environment around the fruit is by the use of different packaging material. Strawberry firmness was maintained in calcium chloride treatments respectively. Storage under influence of calcium increased the firmness of fruits. Same results were found by Garcia et al. (1996) and later confirmed by Asrey and Jain (2006).
The total soluble solids are reported to increase during fruit ripening (Cordenunsi et al. 2002). During the present investigation, total soluble solids were not effected by calcium treatments, the average mean value 6.6 was obtained which is similar to the one cited by Berbari et al. (1994). As the storage period prolongs, the TSS value of fruit increases. During storage, loss of weight is mainly due to the water loss and that lead to high concentration of total soluble solids in fruit (Subedi and Bhattarai 1999).
The storage of fruits at 4 0C maintained the marketable fruit quality for reasonable periods. At room temperature, due to high evaporation and low humidity the total soluble solids increased. Packing of fruit in polythene bags reduced respiration and builds up high humidity around the fruit thus, less water loss occur resulting in fewer disturbances in fruit's total soluble solids concentration. Fruit can be stored for longer time in this condition. In contrast, the fruits stored in cardboard suffer water loss and thus total soluble solid content increased with increase in storage time (Kumar and Manimegelai 1998).
The strawberry fruit is a good source of ascorbic acid (Robards et al. 1999) which is an important quality parameter from the consumer's point of view (Moor et al. 2004).
Ascorbic acid content was higher in fruits stored at 4 0C in cardboard boxes and supplemented with 1.5% calcium chloride. Similar results were reported by Asrey and Jain (2006) that calcium chloride treated fruits were acceptable for higher ascorbic acid content. During the storage the fruits itself might utilize the acid so that the acid in the fruit during storage period decreased. This change in ascorbic acid concentration was mainly due to the metabolic activity of living tissue during which depletion of acid take place and ultimately, total sugars and total soluble sugars increased. At room temperature this activity was more rapid than in refrigeration storage. Strawberries stored for 13 days at 4 0C had high ascorbic acid level then fruits stored at room temperature which were last for 3 days. The ascorbic acid level of strawberries placed in polythene bags at room temperature was higher because of modified atmosphere inside the bags.
The reduction of total titrable acidity in strawberries during storage might have been result of acid oxidation during the Kreb's cycle, once that this constitutes an excellent energy reserve for the fruit. The 4 0C maintained the total titrable acidity and slowed the rate of decline whereas, prominent decline occurred in treatments kept at room temperature due to rapid metabolic activities of living tissues. Decrease in total acidity and increase in total sugars during storage at room temperature was observed by Ramana et al, (1979). The reduction in acidity was higher in fruits stored at room temperature (Kumar and Manimegelai 1998).
Fruit packed in polythene bags maintained high humidity during storage which was proved more beneficial at 40C because humidity reduce the rate of respiration and water loss and improved the micro climate of the fruit as result the shelf life and quality of fruit increased. At room temperature the high humidity inside the polythene bag caused fungal attack and softening of fruit. Similarly cardboard packing caused drying in refrigeration and reduced the chances of fungus at room temperature for couple of days but fruit shriveling was observed with increase in days of storage.
Calcium chloride minimized the chances of infection on fruits. This probably be because that calcium incorporates into the cell wall of the fruits conferring high resistance of infection (Wang et al., 1993).
During the year 2008, the weight loss showed positive and significant correlation with TSS (r=0.414**), fiuit firmness (r=0.905**) and ascorbic acid (r=0.407**). Similar correlation was also observed during 2009. During 2009, fruit firmness exhibited positive and significant correlation (r=0.402**) with ascorbic acid content.
It can be inferred that storage of strawberry fruits at 4 0C and dipping in calcium chloride (1 and 1.5%) solution and packing in polythene bags can be highly effective in improving the shelf life of strawberry fruits.