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Striga hermonthica Seed Inoculum Rate Effects on Maize Hybrid Tolerance and Susceptibility Expression

International Agriculture Research Inst., Kyungpook National Univ., Taegu, 702-701, South Korea
Dep. of Agronomy, Univ. of Ibadan, Ibandan, Nigeria

^* Corresponding author (kimsk{at}bh.kyungpook.ac.kr).

A parasitic plant, Striga hermonthica (Del.) Benth., infests millions of hectares of arable land in sub-Saharan Africa, and it threatens production of major cereal crops including maize (Zea mays L.). Erratic natural infestation is considered a major constraint to assess host plant resistance to the parasite. The objective of this study was to evaluate the effects of different S. hermonthica seed inoculum rates on a tolerant and a susceptible maize genotype. Individual maize plants of the tolerant (8322-13) and the susceptible maize hybrid (8338-1) were inoculated with six rates of germinable Striga seeds: 750, 1500, 2250, 3000, 3750, and 4500. Uninfested plots served as the control. The experiment was conducted at two locations, Mokwa (two seasons) and Abuja (one season), in Nigeria. Increasing Striga inoculum level increased Striga emergence and the amount of damage to the host plant, plant height, and grain yield of the host crop. The tolerant hybrid showed less host plant damage (P < 0.01) and that fewer S. hermonthica plants emerged (P < 0.05) than the susceptible hybrid. Among the four traits studied, host plant damages core was most correlated with grain yield (r = –0.65**). Average grain yield of the tolerant hybrid, 8322-13, was 97% higher than that of the susceptible hybrid, 8338-1, across the six inocolum rates. The tolerant hybrid produced similar grain yields under all levels of the inoculum; the yield reductions ranged from 27% (2250 seeds) to 35% (4500 seeds), while the yield reduction of the susceptible hybrid ranged from 43% (750 seeds) to 74% (3750 seeds). Based on the results this study, we conclude that host plant tolerance is the key element for stabilizing crop yield under S. hermonthica infestation.

Received for publication October 10, 1995.