First report of stem blight and leaf spot in horse purslane caused by Gibbago trianthemae in Sinaloa, Mexico

Horse purslane (Trianthema portulacastrum L.) is a common weed in Mexico, where it competes with different agricultural crops and grows along watercourses, railways and roadsides, abandoned fields, and urban communities. In Sinaloa, this weed grows abundantly during the rainy season (July–September) and competes with summer crops such as corn and sorghum during the fall-winter season, and with common bean and corn mainly in alluvial soils. In recent years, horse purslane has suffered a 100% incidence of stem blight and leaf spot, with a diseased foliar area ranging from 35% to 80%. Ten isolates of an unknown fungus were obtained from symptomatic tissue and identified as Gibbago trianthemae Simmons, based on morphological features of the anamorph, with this identification confirmed in nine isolates by ITS rDNA sequence analysis. The identity of the fungus coincides with previous reports from other parts of the world, where it causes symptoms on horse purslane similar to those described here. In particular, due to its host specificity and aggressiveness towards horse purslane, G. trianthemae has been considered as a potential mycoherbicide. The pathogenicity of six fungal isolates was demonstrated according to Koch’s postulates. Our study provides new research directions for determining host specificity, obtaining aggressive strains, establishing the most appropriate inoculum levels, and demonstrating the influence of climatic conditions on the severity of the disease, which will help to assess the utility of the pathogen as a potential mycoherbicide.