ABSTRACT
Stalk rot is frequently observed in maturing, rust-infected pearl millet (Pennisetum glaucum). Fungi were isolated from internal stalk tissue, and their association with node discoloration and rust infection at different stages of plant maturity was determined to gain a greater understanding of stalk rot etiology. In 1995, stalk rot was observed in a breeding population of pearl millet. Stalks of 10 rust-infected plants were collected on each of three dates during grain fill. Frequency of symptomatic, discolored nodes was higher in the later sampling dates. Stalk sections from 119 discolored nodes were surface sterilized and plated onto agar media. Fungi most frequently isolated from symptomatic nodes were Bipolaris setariae (isolated from 47% of discolored nodes), Fusarium semitectum (28.6%), and F. moniliforme sensu lato (23.5%). Isolation frequency of these fungi differed (P < 0.05) with sampling date. In 1996 and 1997, the hybrid HGM 100 was evaluated at two dates of planting in each year. Ten stalks were sampled at each of four growth stages: panicle emergence, stigma emergence, milk, and hard dough. A total of 140 stalks was assessed for rust severity and for internal stalk discoloration at the nodes. The frequency of discolored nodes increased with plant maturation and was correlated (P < 0.01) with severity of rust infection. All nodes were plated on an agar medium, and a total of 1,512 isolates from 30 fungal genera or species were isolated from the 1,540 nodes of the sampled stalks. F. moniliforme was isolated most frequently (isolated from 23.5% of all nodes). Frequency of isolation of F. moniliforme from nodes within stalks increased with advancing maturity in the earlier dates of planting, but was not correlated with rust infection. B. setariae (isolated from 9.2% of all nodes) was more frequently isolated from plants at the dough stage in three plantings, and was correlated (P < 0.01) with rust severity. Trends in the frequency of isolation of other fungi were inconsistent between planting dates or among growth stages. Frequency of isolation of F. semitectum (isolated from 11.0% of all nodes) and Alternaria spp. (6.9% of all nodes) was correlated (P < 0.05) with rust severity. Frequency of isolation of Curvularia spp. (isolated from 7.0% of all nodes) was negatively correlated (P < 0.05) with rust severity. Isolation of Alternaria spp. and B. setariae was more frequently associated with node discoloration than was isolation of the other fungi. Stalk rot of pearl millet is the result of a complex of several fungi whose incidence was influenced by rust infection, plant maturation, and environmental factors associated with differences among years and dates of planting.
