FUNGAL PATHOGENS AND THEIR INFLUENCE ON PROTEIN CONTENT IN BARLEY GRAINS

Abstract

Barley (Hordeum vulgare) is an annual cereal crop and is ranked fourth in terms of production and utilization after maize, rice and wheat. Its main economic usage all over the world is for malt production. Good quality malt requires strict protein content with a narrow optimum range of between 9.5 to 11.5 %. When this is modified, the malt quality is compromised. Production challenges especially from pests and diseases affect the malt quality. The most prevalent barley diseases in Kenya are net blotch (Pyrenophora teres), scald (Rhynchosporium secalis) and infections from Fusarium species. The aims of this research were to assess the morphological diversity of Fusarium species in major barley production areas of Kenya such as Mau Narok, Njoro and Moiben, to determine the severity levels of fungal infection in four commonly grown barley varieties in Kenya and to determine the extent to which these pathogenic infections influence protein content modification in barley grain. Assessment of morphological diversity and identification of Fusarium species was done by visual microscopic observation of cultures and data taken on conidia shape, mycelium colour, substrate colour and septation of mycelium. Data on disease severity was collected on a 0 to 9 scale and used to determine the level of pathogenic infection amongst the barley varieties. The data was then subjected to analysis of variance using Genstat software version 14.0 and significant differences tested at 5% level of significance. Influence of the three pathogenic fungi of interest through severity levels amongst the barley varieties was used to indicate the degree of protein content modification by the level of diversion from the required protein content optimum range. The findings indicated that there are six morphologically diverse groups of Fusarium species in the barley growing regions in Kenya with F. poae being the most prevalent across all regions. The varieties had varied levels of severities from pathogenic infections leading to varied proportions of protein content modification. The most tolerant varieties had their grain protein content least modified by the pathogenic fungi effect. P. teres, R. secalis and F. poae had a profound influence in modification of protein content in the barley grains which is a key determinant of malt quality. Severity levels below 20% foliar infection from all the pathogenic fungi observed in all the varieties did not have a significant impact in modifying the protein content from the required optimum range. Managing these diseases to below 20% infection and using disease tolerant barley varieties will ensure required malt quality parameters are attained.