Studies on Seedborne Nature and Management of Alternaria alternata and A. brassicae in Pigeonpea
Four pigeonpea accessions (ICP 12108, ICP 13446, ICP 13448 and ICP 13271) that had shown 90% seed infection by Alternaria spp. during the seed health testing in 2005 at Plant Quarantine Laboratory (Patancheru, Andhra Pradesh, India) were used for detecting the seedborne nature of Alternaria spp. Seeds of accession ICPL 87051 was used as the resistant control (3% infection). Tricyclazole 75% at 2 g/kg seed, iprodione 25%+carbendazim 25%, thiram and benomyl+thiram (1:1) each at 3 g/kg seed were used for seed dressing. Two species of Alternaria, A. alternata and A. brassicae, were detected in seeds of the 4 accessions. Seed colonization ranged from 76 to 85% by A. alternata and from 15 to 23% by A. brassicae across the susceptible accessions, whereas the infection in the resistant control was only 3% by A. alternata and there was no infection of A. brassicae. The overall seed germination ranged from 18 to 29% in infected seeds across the genotypes, whereas it was 81% in the resistant control. There was a significant negative correlation between germination and infection (r=0.90). Component plating revealed that seed coat recorded 100% infection by both the species of Alternaria in all 3 genotypes (ICP 12108, ICP 13271 and ICP 13446). A. alternata infection in cotyledons varied from 76 to 86%, and in embryos from 3 to 8%, except in ICP 12108 and ICPL 87051. A. brassicae infection in seed cotyledon ranged from 3 to 9% whereas in embryo it was 2% only in ICP 13446. The iprodione 25%+carbendazim25% and mixture of benomyl and thiram proved the most effective in reducing the internal seedborne infection by Alternaria spp. Iprodione 25%+carbendazim25% showed the maximum seed germination.