Morphological identification of the ryegrass hybrid Lolium multiflorum × Lolium perenne and isolation of the pathogen Fusarium pseudograminearum in the Western Cape

Abstract

Weed resistance to herbicides present one of the greatest current economic challenges to agriculture. Herbicide resistant ryegrass (Lolium spp.) is a serious problem in Western Cape grain-producing areas. Morphological and pathogenic analyses were performed on ryegrass samples. Morphologically, 50% of specimens were classified as rigid ryegrass, 48% as a hybrid, namely L. multiflorum × L. perenne and 2% as perennial ryegrass. Fusarium pseudograminearum (cause of Fusarium crown rot) was isolated from six localities. Pathogencity tests confirmed that F. pseudograminearum isolates obtained from ryegrass and wheat are pathogenic on both crops, indicating that ryegrass can act as an alternative host and a source of inoculum of this important soilborne pathogen. Grass weed infestation can favour the disease, and grass weed control is therefore recommended as part of an integrated strategy to manage crown rot. Knowledge on morphological differences among ryegrass may be important to guide differential weed management of ryegrass. Smother cropping, as part of conservation farming, should receive more prominence to suppress herbicide-resistant ryegrass and simultaneously reduce the occurrence of crown rot.