Host Biotic Factors Affecting Virulence of Corn Cyst Nematode, Heterodera zeae on Corn in Egypt

Abstract

Four biotic factors respecting the corn plant affect the virulence of the corn cyst nematode, Heterodera zeae such as corn genotype, corn age, corn nutritional status, and cropping sequence regime. For the first factor, when two local corn cultivars, namely, Giza 2 (susceptible) and Kahera 1 (resistant), were subjected to the infection by H. zeae to determine the biotic effect of the host susceptibility on development and reproduction of the nematode, the final population and rate of build-up of the nematode were more remarkable on Giza 2 cultivar than on Kahera 1. Due to the high suitability of Giza 2 for nematode reproduction, there was more pronounced damage to plant growth in Giza 2 than in Kahera 1. As for the second factor, the nematode final population and rate of buildup correlated negatively with the host age, which multiplied highly and was more virulent on the youngest seedlings than on the oldest plants. Studies on the effect of N, P and/ or K fertilizers applied to Giza 2 corn on the behaviour of H. zeae revealed that the nematode population greatly varied according to the fertilizer type and level. When N, P, or K were used separately, the fertilized plants sustained the lowest nematode final population and rate of build-up as compared with those of the control plants; however, the recommended levels of these fertilizers caused the lower values amongst the applied fertilizers levels and achieved higher increase in the plant growth parameters. As for the N, P, and K used in different combinations, a similar trend was noticed when the recommended levels of the fertilizers were applied to plants. It is worthy of notice that when phosphorus was decreased or nitrogen increased, in combination with the other elements at their recommended levels, the nematode reproduced well and folded several times. Also, population dynamics of juveniles and cysts of H. zeae under the stress of a cropping sequence regime revealed that the average number in each stage greatly fluctuated. The density of juveniles or cysts gradually increased with the favorable host (Giza 2 corn) to reach its peak at the crop maturity, while the nematode population dropped sharply when the field became fallow. Likewise, the population densities of the previous stages declined gradually, even in the presence of the non-host crop (Egyptian clover CV. Meskawii).