Dynamics of Moisture, Nitrogen, and Striga Infestation on Pearl Millet Transpiration and Growth

Abstract

AbstractThe parasitic weed Striga hermonthica (Del.) Benth. (witchweed) is a major biotic constraint to pearl millet [Pennisetum glaucum (L.) R. Br.] production in Sahelian Africa. To address this constraint, more information is needed on host‐parasite relations under varying conditions of soil water and nutrient availability typically found in the Sahel. The dynamics of moisture, N, and Striga infestation on pearl millet transpiration and growth were investigated. The effects of Striga infestation, water deficit stress, and N availability on root length and dry weight, shoot dry weight, and transpiration ratio (TR; g dry matter kg−1 transpiration) were evaluated. Millet was grown in 36‐L pots for 45 d in a glasshouse, using two levels of water and N availability and three levels of Striga infestation. With no N, shoot dry weight of uninfested millet plants was low. Shoot weight was further reduced by 42% at the high level (71 000 seeds pot−) of Striga infestation. With the addition of 60 kg ha− of N, shoot weight of uninfested millet plants increased five‐ to sixfold. A reduction of 36% in shoot weight was observed in plants with N and highest infestation of Striga. Root dry weight was also low without N, but unaffected by Striga infestation. With the addition of N, root dry weight of millet plants increased under adequate and water‐stressed conditions. Root length in the upper 0.10 m followed a similar trend. Transpiration ratio decreased due to Striga infestation, increased with reduced water availability, and increased with greater N supply. The number of Striga haustoria attached to millet roots increased with water deficit stress, N addition, and increased level of infestation. The number of haustoria per unit root length increased with water stress and Striga infestation, but was substantially decreased by N addition. The number of haustoria per unit root length increased linearly with the total number of haustoria present. This slope was independent of water supply, but was four times greater for unfertilized plants compared with those receiving N. This study confirms that Striga attack is more severe in the presence of nutrient and water stress, and reduces whole‐plant water‐use efficiency. It also suggests a physiological mechanism by which N addition permits the host to better resist Striga attack.