Location: Vegetable ResearchTitle: Tolerance to powdery mildew conferred in susceptible watermelon scion by grafting on resistant rootstocks
Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: 2/11/2015
Publication Date: N/A
Interpretive Summary: N/A
Technical Abstract: Cucurbit powdery mildew (PM) caused by Podosphaera xanthii, can impact seedling growth and cause serious losses in greenhouse and open field production. We have developed several watermelon and bottle gourd germplasm lines with high levels of resistance to PM. A PM susceptible cultivar Mickey Lee was grafted on these PM resistant germplasm that were used as rootstocks. USVL677-PMS, a watermelon line, and USVL848-PMS, a bottle gourd line, were used as susceptible rootstock controls. Each grafted rootstock was replicated eight times with four plants per replication. Grafted plants were inoculated by spraying with a PM melon race one conidial suspension (2 x 104 conidia/mL) in sterile water (0.02% Tween 20). Grafted plants were rated for PM severity on a 0-10 scale when severe PM was observed on susceptible checks, generally 10-14 days after inoculation. Severe powdery mildew was observed on cotyledons of USVL677-PMS and USVL848-PMS. Significantly less, no PM was observed on cotyledons of PM resistant rootstocks. Severe PM was observed on cotyledon and leaves of the scion (Mickey Lee) cotyledon grafted on susceptible rootstocks. Significantly (P=0.001) less PM was observed on the second, third and upper true leaves of Mickey Lee plants grafted on some PM resistant watermelon rootstocks compared to susceptible rootstocks. Powdery mildew on true leaves was significantly less on Mickey Lee grafted on, two PM resistant bottle gourd rootstocks (USVL351-PMR and USVL482-PMR), and a bottle gourd hybrid rootstock (USVL482351-PMR-F1). Not all PM resistant watermelon germplasm lines conferred resistance to true leaves of Mickey Lee.