MEXICO CITY, MEXICO
CIMMYT

Evaluation of tropical inbred lines for resistance to Fusarium moniliforme ear rot
--D. Jeffers, S. K. Vasal, S. McLean, G. Srinivasan

Advanced lowland tropical maize inbred lines developed at CIMMYT were evaluated for resistance to Fusarium moniliforme ear rot in a preliminary study in Poza Rica, Vera Cruz during the 1993A growing season using one, 5 m row subplots. Two inoculation treatments were used to compare infection levels: 1) the nailpunch/sponge technique with a spore suspension of 5.0 x 105 spores/ml applied through the husk in the middle of the ear (Drepper et al., Plant Dis. 74:952-956, 1990), and 2) application in the silk channel of a 1 ml spore suspension of 5.0 x 105 spores/ml prepared in a 4 M sucrose solution. Inoculations were made 7-10 days after 100% extrusion of the silks. Ears were evaluated at physiological maturity using a visual rating scale of 1-6 for percent infection (1=0%, 2?10%, 3?25%, 4?50%, 5?75%, and 6?100%). A total of 164 lines, including 58 announced CIMMYT maize lines (CML), and 53 promising lines from both white and yellow grain type, were evaluated. From the 1993A results 23 inbreds with the lowest levels of F. moniliforme infection and 2 lines used as checks were evaluated in 1993B in a split plot design using the same two inoculation techniques and 4 replications. Subplots were one, 2.5 m row. The purpose of this trial was to evaluate the lines for resistance to infection, to determine if the sucrose solution method improved the level of infection compared to the standard nailpunch technique presently being used, and to determine if there was a correlation between the two techniques. Results obtained indicate that the sucrose technique was significantly better than the standard nailpunch technique (p=0.05) as determined by Fisher's LSD test for percent infection. The correlation between the rankings of the lines for resistance to ear rot with the two techniques was 0.81. Five inbreds in the evaluations had ratings between 2 and 3 with the two treatments and are considered to have high levels of resistance to F. moniliforme ear rot infection. An additional 3 lines are included which had low ear rot ratings from earlier evaluations. Another season of ear rot evaluations will be performed with these lines to confirm our results. The lines are:

CML 48 Porillo 8073-11-1-1-##
(Pop 22 TSR)-4-3-1-3-1-BB-####
CML 52 Sta Rosa 8079-22-2-2-##
CML 1 Pop 21 C5 HC57-1-2-B-##
Sint Am TSR-76-1-1-1-2-BB-####
(Across 7643 x 43 F7)-2-3-4-3-BB-####
CML 40 Pop 36 C5 HC144-2-2-B-###
Sint Am TSR 23-3-1-2-3-BB-#### 


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