Identification of non-nodulating, and low and high nodulating plants in pigeonpea

A glasshouse screening program was initiated to identify non-nodulating (Nod−) plants in pigeonpea (Cajanus cajan L. Millsp.). A visual rating scale of 1 (minimum nodulation) to 5 (maximum nodulation) was developed that allowed rapid screening of large numbers of plants. The scale correlated significantly (r = 0.89–0.94, P < 0.001, n = 24) with nodule number and nodule mass. No Nod− plants were identified even after screening 100,000 plants involving five cultivars and advanced breeding lines. However, Nod− plants were obtained from F2 populations of six different crosses. Progeny of these selections when selfed to F3 or to F5 remained Nod−. Plants with a low and high capacity for nodulation were also identified within particular cultivars and advanced breeding lines. After two cycles of pure line selection in the glasshouse progenies of selected materials maintained their relative nodulation ratings when planted in a field of low mineral N (about 10 mg kg−1 soil).