Effect of plant architecture on levels of Helminthosporium sativum infection on spring wheat grown in Zambia

Abstract

Spot blotch disease ( Helminthosporium sativum Pamm., King & Bakke) is a serious constraint to wheat production in the warm humid tropics. Disease escape mechanisms such as plant height act to make selection of genetically resistant material difficult. A trial was designed to quantify the relationship between height and levels of spot blotch on the flag leaves and ears. Flag leaf and ear disease levels were negatively correlated ( r = −0·64 ∗∗ ) with yield. Flag leaf disease level was also negatively correlated with plant height ( r = −0·40 ∗∗ ), last internode length ( r = −0sd34 ∗ ) and peduncle length ( r = −0·62 ∗∗ ). Ear disease level was significantly correlated with last internode length ( r = −0·46 ∗∗ ), but not with either plant height ( r = −0·23) or peduncle length ( r = −0·26). The results show that the greater the distance between the leaves below the flag leaf and the flag leaves and ears, the lower the levels of spot blotch on those organs. The low coefficients of dispersion for height, and flag leaf (0·16) and ear (0·09) disease levels, indicate that resistance is, at least in part, genetically determined and that selection of shorter plants with resistance to spot blotch should be possible. In environments where disease pressure is very high, height could be used to augment genetic resistance.