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To understand the impacts of increase UV-B radiation on nematode populations, Date palm Phoenix dactylifera plants will expose to three levels of UV-B radiation [0 (control), 6 and 12 kJ m−2 day−1] in a glasshouse from seedlings of 2 year old date palm. At each UV-B treatment, four populations [0 (N0), 2500 (N2500), 5000 (N5000) and 7500 (N7500)] of nematodes will incorporate into the sterilized rooting medium. Plant growth, development, photosynthetic parameters, pigments, phenolics and the number of eggs and nematode numbers in the rooting medium will record at the end of the experiment.
The United Arab Emirates is the world's largest exporter of dates. In 1999, the UAE produced 305,000 MT (about 6% of the global production) and exported approximately 189,200 MT (about 42 percent of the global date export market of that year), i.e. exported about 62 percent of the annual production (Quinlan, and Dhouibi, 2006). In 2003, UAE production rose to 757, 601 MT. The Abu Dhabi Emirate is by far the largest producer of dates in the United Arab Emirates where there are approximately 33 million date palms. There are approximately 7.7 million palms in the other six Emirates. However, of Abu Dhabi's 33 million palms, only 13.8 million are currently producing (UAE Agriculture Statistics Year Book), the rest are young date palms growing on many hundreds of new farms; these palms will not produce significant crops for another three to five years. When they do, the United Arab Emirate's date production could match that of Saudi Arabia (Quinlan, and Dhouibi, 2006).
Date-producing oases in the United Arab Emirates are made up principally of female palms, which are the ones that bear fruit. The male plants and high quality pollen is imported. Even now, it is not uncommon for growers to select spathes of male pollen from the market. The spathes containing pollen appear in February/March and last until early April. Since natural pollination depends on wind and insect vectors and since these means result in very low levels of fertilization, certainly insufficient for commercial production, growers engage in artificial pollination, both by hand and by the use of mechanical blowers.
Plant-parasitic nematodes cause about $100 billion in crop losses annually. Root-knot nematodes (RKN; Meloidogyne spp.) are sedentary endoparasites that can attack more than 3000 host plant species. The most economically important species, Meloidogyne incognita, is widespread and considered as an important crop pathogen worldwide (Abad et al., 2003).
Root-knot nematodes (Meloidogyne spp.) are widely distributed in date palm plantations. However, the damage has not been determined (Carpenter, 1964). And, no major attempts have been made to control nematode infestation in date palm cultivations. Nematodes are spread by infested offshoots growing below the soil surface. Root-knot nematodes have such a wide range of plants (Zaid et al, 2002). Two species of Longidoridae are described from poorly growing date palms in Saudi Arabia, namely, Longidorus orientalis n. sp., and Xiphinema phoenicis n. sp. (Loof, 1982). In Oman, a survey conducted in 1990-1997 by Mani et al., recorded 12 species of Pratylenchus in 31 plant families including 19 tree fruit crops, 16 field crops, two ornamental crops and 14 weeds (Mani et al., 1997). Ibrahim et al. (2000) surveyed nematode infestation in date palm cultivations in Egypt. Nematodes in 14 genera were extracted from the soil samples from three different regions in Egypt. The most common nematodes were Criconemella sphaerocephala, Hoplolaimus clarissimus, Meloidogyne incognita, and Paratrichodorus minor. Also, in all the samples several unidentified (non-phytoparasitic) nematodes belonging to both Dorylaimid and Rhabditid groups were found. Root-knot nematode (Meloidogyne spp.) was the most common followed by M. javanica.
On the other hand, entomopathogenic nematode (H. indicus) of Heterorgabditis species or steinernema sp. have proven to be natural enemies of red palm weevil (grub stage only) and are being used in the Middle East to control the weevil populations in a symbiosis with Xeonorhabdus bacteria (Zaid et al., 2002).
RNA silencing is a genetic mechanism that triggers degradation of mRNA to regulate gene expression at the post-transcriptional level. RNAi or post-transcriptional gene silencing has been used successfully in the free-living nematode, Caenorhabditis elegans, to silence genes, to study gene function in loss-of-function mutants (Kamath et al., 2003), and to target a number of specific genes of two plant-parasitic cyst nematodes i.e., Heterodera glycines (Alkharouf et al., 2007) and Globodera pallida (Urwin et al., 2002). Alkharouf et al. (2007) identified over 1500 H. glycines genes presumed to be orthologs of essential C. elegance genes that potentially have lethal phenotypes if they are silenced and demonstrated that silencing the ribosomal gene Hg-rps-23 from H. glycines was lethal to the nematode. Ibrahim et al. (2010, submitted) attempted to broaden resistance of soybean against the root-knot nematode M. incognita by silencing the genes encoding L-lactate dehydrogenase (LDH), mitochondrial stress-70 protein precursor (MSP), ATP synthase beta-chain mitochondrial precursor and tyrosine phosphatase (TP) using RNAi gene silencing. These four RKN genes were silenced individually. Agrobacterium rhizogenes was used to transform soybean roots with the RNAi gene constructs. The transformed roots were challenged with RKN where nematode development was examined in the transformed roots. A substantial reduction in the number of galls formed on the roots after one month of infection. The genes targeted by the RNAi have high similarity to C. elegans genes that were predicted to be lethal if silenced and to genes of the soybean cyst nematode (H. glycines) that were over-expressed during feeding (Alkharouf et al., 2007 and Klink et al., 2009b). Silencing the genes encoding TP and MSP greatly decreased gall formation and showed a promising solution for broadening resistance of plants against this plant-parasitic nematode.
Global changes in climate would severely affect human health, natural ecosystem and agricultural crops. To meet the demands of a growing human population, agricultural productivity must continue to increase. If global climate changes, act to reduce food production, serious, long-term food shortages and aggravation of societal problems could result. Elevated levels of ultraviolet radiation (UV-B) from the sun would have very damaging effects on agricultural crops and livestock. The stratospheric ozone layer, which filters abundance of the harmful UV-B before it reaches the earth's surface, has suffered considerable attrition in recent years due to artificial chemicals such as chlorofluorocarbons (CFCs) and methyl bromide which have resulted in increased UV-B. Thus, effects of UV-B radiation on horticulture crops have been comprehensively studied during the last three decades signifying that UV-B is damaging to crops (Kakani et al., 2003). To date, there are only a few studies that have reported UV-B effects on biotic responses in the crop environment. Ballare et al. (1996) found that current levels of UV-B significantly decreased insect herbivory on forage, while Zavala et al. (2008) found that UV-B has an important regulatory effect on the interactions between soybean and leaf herbivory. Also, the increased UV-B radiation reduced herbivory of snails and slugs (Gwynn-Jones 1999). However, there are no studies on UV-B on Date palm and the effects on nematodes, which are pests that significantly reduce yields of crops in major agricultural regions of the world (Sasser, 1989).
The cDNA primers of genes targeted by the RNAi for the genes used in the above mentioned studies can be utilized to screen the following:
The date palm varieties for nematode resistance genes.
The Nematode populations to identify the infecting nematode species.
Conducting these screens on all treatments and control will allow analyzing the results, i.e. whether infestation/non-infestation is due to the UV- B, the genotype or other possible factors.
Examine the effect of UV-B radiation on nematode infestation of date palms.
Screen UAE date palm varieties for nematode resistance.
Screen nematode species infesting date palm varieties utilized.
Duration: Three Years.