The effect of foliage pathogens on growth of peanuts (Arachis hypogaea L.) in tropical Northern Australia

Abstract

The effect of foliage pathogens on growth and development and final yield of Virginia Bunch peanuts was assessed under tropical wet season conditions in the Ord River Irrigation Area. Applications of the fungicides chlorothalonil and benomyl were used to manipulate onset and severity of disease during the season. Heavy disease pressure in unprotected plots caused severe defoliation and a 30% reduction in commercial yield. This yield reduction, associated with significantly lower pod numbers, was probably due to defoliation causing reduced interception of incident photosynthetically active radiation (PAR) during pod fill and reduced efficiency of conversion of intercepted PAR to reproductive yield. The latter was due to the effect of foliage pathogens on either photosynthetic capacity of remaining leaves, or patterns of assimilate distribution. Data on PAR interception and remaining leaf area alone did not adequately explain the effects of foliage pathogens on crop yield. Canopies with maximum disease control maintained leaf area indices well in excess of that necessary for full interception of incident radiation until maturity. However, commercial yields of pods and kernels from these plots were significantly lower than for those with intermediate foliage protection. This effect was probably due to altered patterns of assimilate distribution between vegetative and reproductive plant parts. The rate of increase in kernel size in fully protected plots was lower than in those with less effective pathogen management, so that a greater proportion of the total pod yield consisted of small, immature pods which were lost during the commercial threshing process.