Project Number: 6607-21000-009-14
Project Type: Specific Cooperative Agreement

Start Date: Aug 14, 2007
End Date: Oct 31, 2008

Objective:
The objective of this research project is to screen the USDA Cowpea Core Collection for resistance to cowpea aphid in seedling (greenhouse) and naturally infested field tests, and to complete the screening of the USDA cowpea core collection for resistance to Rk-avirulent and Rk-virulent strains of root-knot nematodes.

Approach:
1) Aphid screening: In seedling screens, two plants of each accession will be established in 1 gal pots filled with sterilized soil mix. Six replicate pots of each accession and of a control susceptible genotype (CB27) will be used. Two-week-old plants will be infested with cowpea aphid larvae, monitored every four days for aphid buildup and plant health, and scored to classify accessions as fully susceptible, moderately susceptible, moderately resistant or highly resistant. In field screens, cowpea accessions will be planted in a replicated trial in single 20 foot rows on 30 inch raised beds with susceptible checks on every third row. Naturally infested cowpea aphid populations will be rated biweekly for resistance five weeks after planting. Intensity of aphid attack and plant health of each accession will be evaluated on a 0-9 scale. 2) Root-knot nematode screening: Two plants of each cowpea accession plus resistant and susceptible checks will be evaluated in a modified growth pouch screening system. Ten-day-old plants in pouches will be inoculated with second-stage root-knot juveniles and after 30 days at 26-27 C, a nematode egg-mass selective dye will be used to stain the egg masses per root system which will be counted to quantify nematode reproduction and classify for resistance. Putative resistant accessions will be re-screened with a minimum of 10 replicate plants per entry with the M. javanica and M. incognita isolates used in the first screen plus additional isolates of M. incognita that express virulence. 3) Data repository: The resistance screening indices from the aphid and nematode screening work will be sent to the USDA in both hard copy and electronically, for entry into the GRIN system database.