Farmer-managed trials in south-east Nigeria to evaluate the rice variety Cisadane and estimate yield losses caused by the African rice gall midge, Orseolia oryzivora Harris & Gagne

Abstract

Farmer-managed trials of the rice variety Cisadane were undertaken at 47 rainfed lowland sites around Abakaliki, south-east Nigeria, a major outbreak area of the African rice gall midge (ARGM). At each site a plot of Cisadane was grown alongside a control plot of the participating farmer's usual variety. On average the Cisadane yielded 26% higher than the controls but ARGM infestation levels on it were only slightly lower, suggesting thatithad greater tolerance to the pest butlittle antixenotic or antibiotic resistance. For all of 14 evaluation criteria, most participating farmers rated Cisadane as better than their control varieties. It appears to be a useful component for an ARGM management strategy. Regression analyses of yield on alternative variables for ARGM infestation derived from data recorded at 3, 7 or 11 w.a.t. (weeks after transplanting) showed that the log-transformed percent tiller infestation at 7 w.a.t. was the best predictor of yield. Variables for site topography, water level, fertilizer use in the nursery, and plant spacing also had significant partial regression coefficients. Excluding plots with tiller infestation levels above 30%, the relationship between yield and infestation was approximately linear and suggested a yield loss of 2.9% per 1% increase in infestation.