Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2008
Publication Date: 6/4/2008
Citation: Kousik, C.S., Levi, A., Ling, K., Wechter, W.P. 2008. Potential Sources of Resistance to Cucurbit Powdery Mildew in US Plant Introductions (PI) of Lagenaria Siceraria (bottle gourd). HortScience. 43(5):1359-1364 Interpretive Summary: Powdery mildew is an important foliar disease that can cause severe damage to plants in the pumpkin and watermelon family grown in open fields and greenhouses. In recent years, there has been a growing interest in the USA in grafting watermelon plants onto bottle gourd rootstocks for managing root diseases. During spring and summers of 2006, we observed bottle gourd plants from commercial seed companies with severe powdery mildew, thus reducing their value as a rootstock. In this study, we tested many wild bottle gourd plants collected from different regions of the world for their reaction to powdery mildew in the greenhouse and laboratory. None of the plants from the wild bottle gourd collection were immune to powdery mildew. However, we identified several bottle gourds with moderate levels of resistance to powdery mildew. These wild bottle gourds will be useful as a source of resistance to breeders for developing superior bottle gourd rootstocks that are resistant to powdery mildew.
Technical Abstract: Powdery mildew (Podosphaera xanthii) can cause severe damage to cucurbit crops grown in open fields and greenhouses. In recent years, there has been a growing interest in the USA in grafting watermelon plants onto various cucurbit rootstocks. Bottle gourd plants (Lagenaria siceraria) are being used throughout the world as rootstocks for grafting watermelon. Although gourd plants are beneficial, they may still be susceptible hosts to various soil-borne and foliar diseases. Bottle gourd plant introductions (PI) resistant to diseases and pests can be valuable source of germplasm in rootstock breeding programs. We evaluated 234 U.S. PI of L. siceraria for tolerance to powdery mildew in the two greenhouse tests. Young seedlings were inoculated by dusting powdery mildew spores of melon race 1 on the leaves and cotyledons. Plants were rated two weeks after inoculation using a 1-9 scale of increasing disease severity. Although none of the L. siceraria PI were immune to powdery mildew, several PI had significantly lower levels of powdery mildew severity compared to susceptible watermelon cultivar Mickey Lee that was rated >7, with a mean of 7.5. The experiment was repeated with 26 select PI on whole seedlings and leaf disks. Significant variability in the level of resistance to powdery mildew on plants within PI was observed. Moderate resistance in several PI to powdery mildew was confirmed. PI 271353 can be considered the most resistant to P xanthii race 1 among the L. siceraria accessions evaluated in this study. The results of our studies suggest that novel sources of resistance could be developed by careful selection and screening of several of the PI with moderate resistance described in our study.