Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2009
Publication Date: 10/10/2009
Citation: Ling, K., Harris-Shultz, K.R., Meyer, J.D., Levi, A., Guner, N., Wehner, T.C., Bendahmane, A., Havey, M.J. 2009. Non-synonymous single nucleotide polymorphisms in the watermelon eIF4E gene are closely associated with resistance to Zucchini yellow mosaic virus. Theoretical and Applied Genetics. 120:191-200.
Interpretive Summary: United States is among the leading watermelon producing countries in the world, with a total production of 4.3 billion pounds and a fresh market value of $434 million in 2007. The aphid-borne Zucchini yellow mosaic virus (ZYMV) spreads rapidly in the fields and is difficult to control. This virus causes serious damage to watermelon, with up to 50% yield losses in some years. The best strategy to control this virus is by developing and using virus-resistant cultivars. Recently, the USDA watermelon plant introduction collection was evaluated for ZYMV resistance and several PIs were found to be ZYMV resistant. In this study, we conducted genetic and molecular experiments, and identified and developed a DNA-based marker that is closely linked to the gene conferring ZYMV resistance in watermelon. This DNA-based marker can be used in watermelon breeding programs to develop ZYMV-resistant cultivars. The use of this methodology would increase selection efficiency and allow plant breeders to develop ZYMV-resistant watermelon cultivars in significantly less time than needed using traditional methods. Developing ZYMV-resistant watermelon cultivars would directly benefit U.S. watermelon growers and consumers by preventing yield losses and maintaining watermelon fruit quality. Additionally, the environment will be protected from the less input in chemical insecticides to control insect vectors.
Technical Abstract: Zucchini yellow mosaic virus (ZYMV) is one of the most economically important potyviruses infecting cucurbit crops worldwide. Using a candidate gene approach, we cloned and sequenced eIF4E and eIF(iso)4E gene segments in watermelon. Analysis of the nucleotide sequences between the ZYMV-resistant watermelon plant introduction PI 595203 (Citrullus lanatus var. lanatus) and the ZYMV-susceptible watermelon cultivar ‘New Hampshire Midget’ (‘NHM’) showed the presence of single nucleotide polymorphisms (SNPs). Initial analysis of the identified SNPs in association studies indicated that SNPs in the eIF4E but not eIF(iso)4E were closely associated to the phenotype of ZYMV-resistance in 70 F2 and 114 BC1R progenies. Subsequently, we focused our efforts in obtaining the entire genomic sequence of watermelon eIF4E. Three SNPs were identified between PI 595203 and NHM. One of the SNPs (A241C) was in exon 1 and the other two SNPs (C309A and T554G) were in the first intron of the gene. SNP241 which resulted in an amino acid substitution (proline to threonine) was shown to be located in the critical cap recognition and binding area, similar to that of several plant species resistance to potyviruses. Analysis of a cleaved amplified polymorphism sequence (CAPS) marker derived from this SNP in F2 and BC1R populations demonstrated a cosegregation of between the CAPS-2 marker and their ZYMV resistance or susceptibility phenotype. When we investigated whether such SNP mutation in the eIF4E was also conserved in several other PIs of C. lanatus var. citroides, we identified a different SNP (A171G) resulting in another amino acid substitution (D71G) was identified from four ZYMV-resistant C. lanatus var. citroides (PI 244018, PI 482261, PI 482299 and PI 482322). Additional CAPS markers were also identified. Availability of all these CAPS markers will enable marker-aided breeding of watermelon for ZYMV resistance.