GENETICS AND GENETIC IMPROVEMENT OF DISEASE RESISTANCE AND QUALITY TRAITS IN WATERMELON, BROCCOLI, AND LEAFY GREEN BRASSICAS
Location: Vegetable Research
Title: Genetic diversity among Lagenaria siceraria accessions containing resistance to root-knot nematodes, whiteflies, ZYMV or powdery mildew
Submitted to: Plant Genetic Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2008
Publication Date: March 5, 2009
Citation: Levi, A., Thies, J., Ling, K., Simmons, A.M., Kousik, C., Hassell, R. 2009. Genetic diversity among Lagenaria siceraria accessions containing resistance to root-knot nematodes, whiteflies, ZYMV or powdery mildew. Plant Genetic Resources: Characterization and Utilization 7(3):216-226. http://journals.cambridge.org/action/displayFulltext?type=1&fid=6642268&jid=PGR&volumeId=7&issueId=03&aid=6642260
Interpretive Summary: The bottle gourd, Lagenaria siceraria, is one of the early vegetable crops domesticated by man. Bottle gourds grow in different parts of the world and have resistance to important diseases and pests of cucurbit crops (including watermelon and melon). For these reasons, bottle gourds are used in Asia as rootstocks (the lower part of the plant stem with a healthy root system) for grafting watermelons. There is a growing interest in grafting watermelon plants on bottle gourds to reduce the occurrence of diseases and pests in watermelon fields in the U.S. Over 235 bottle gourd varieties, collected in different parts of the world, are being maintained by the U.S. Department of Agriculture, Agricultural Research Service (USDA, ARS), The Plant Genetic Resources Conservation Unit (PGRCU), Griffin, Georgia. However, there is little information about genetic differences and resistance to diseases and pests among these bottle gourd varieties. In this study, we used DNA markers to evaluate genetic differences and conducted experiments to test for pest resistance among these bottle gourd varieties. The genetic analysis revealed that bottle gourd varieties from the same geographical region shared similar genetic background. There were three main groups: 1) African, 2) Asian, and 3) North and South American. A few varieties that were collected in South Asia (India) were resistant to important viruses and diseases of cucurbit crops, while a few varieties that were collected in South and Central America were less infested with root-knot nematodes. Findings from this study will be useful to plant breeders who are trying to develop superior bottle gourd varieties resistant to diseases and pests.
In recent years, there has been an increased interest in Europe and in the U.S. in grafting watermelon onto bottle gourd, Lagenaria siceraria (Mol.) Standl. In this study, genetic diversity and relationships were examined [using 240 sequence related amplified polymorphism (SRAP) markers] among 56 United States Plant Introductions (PIs) of L. siceraria and PIs of important cucurbit crops, [including Cucurbita maxima Duchesne (winter squash), Cucurbita pepo L. (squash and pumpkin), Citrullus spp. (watermelon), Cucumis melo (melon) and Cucumis sativus (cucumber)]. The analysis showed that L. siceraria is distinct and has similar genetic distances to the cucurbit species examined herein. The L. siceraria PIs were assembled into two major clusters. One cluster includes groups of PIs collected mostly in South Asia (India) and a few PIs collected in the Mediterranean region and in Northeast Africa. The second cluster includes groups of PIs collected mainly in Southern Africa and in North, Central, and South America, and PIs collected in China, Indonesia, and Cyprus. All L. siceraria PIs in this study were susceptible to the southern root knot nematode [Meloidogyne incognita (Kofoid & White) Sandground]. However, several PIs, among them a group of closely related PIs collected in Mexico and Florida, were less infected with southern root knot nematodes. All L. siceraria PIs were infested with whiteflies [Bemisia tabaci (Gennadius)], while several PIs were less infested then others and need further evaluation and selection for developing breeding lines that may be less appealing to this pest. Most of the PIs that were collected in India and were found to be resistant to zucchini yellow mosaic virus (ZYMV) and tolerant to powdery mildew appeared to be closely related and belong to the same phlogenetic group. Experiments with L. siceraria rootstocks (PIs) representing different phylogenetic groups showed similar grafting compatibility with watermelon. Findings from this study should be useful for the development of superior L. siceraria rootstock lines with enhanced resistance to diseases and insect pests of cucurbit crops.