Phurejas potatoes (Solanum phureja Juz et Buk) are cultivated in very restricted areas of the Bolivian Andes. Late blight caused by Phytophthora infestans is a destructive, endemic disease that affects the survival and cultivation of this crop. The aim of this study was to determine the resistance characteristics of phurejas potato varieties to P. infestans in a traditional area of cultivation. An experimental plot was prepared in the locality of Chojchoni (3200 m) and planted with different phurejas varieties: 1) Chojllu Phureja (Sste); 2) Phureja Amarilla (Sphu); 3) Polo Phureja (Sphu); 4) Phureja Roja (Sphu); 5) Phureja Negra (Sphu) and 6) Waych'a Paceña (Sadg), a susceptible control. Severity was assessed according to the criteria of the Centro Internacional de la Papa, determining the area under the disease progress curve (AUDPC). Regression analysis (log N disease severity against time) was performed using the logistic model [ln(y/1 − y)] to determine infection rates. The different varieties showed different levels of resistance. The disease progress curve, the AUDPC and the linear regression results revealed the varieties Chojllu Phureja, Phureja Amarilla and Polo Phureja to likely have larger copy numbers of minor resistance genes against P. infestans than Phureja Roja or Phureja Negra. Late blight caused by P. infestans could cause the long-term loss of some phurejas varieties through farmers selecting others less severely affected by the disease.
En la región andina tradicional de Bolivia (>4.000 msnm) donde existen áreas importantes de producción de papa, Septoria lycopersici (conocida como Khasahui) causa pérdidas en la producción de este cultivo. Los objetivos de esta investigación fueron: evaluar el efecto de diferentes fungicidas en el control de la enfermedad estimándose la intensidad (incidencia y severidad) de la enfermedad, y las pérdidas causadas por S. lycopersici en variedades nativas comerciales. Se establecieron parcelas experimentales durante dos años agrícolas (1999/2000 y 2002/2003) en una zona Altoandina húmeda y fría (4.290 msnm) del departamento de La Paz. Se evaluaron los fungicidas: Mancozeb (Dithiocarbamato), Champion (Oxicloruro de Cobre), Bravo 500 (Clorotalonil) y Control (H2O) y las variedades andigena Waych´a Paceña e Imilla Negra (Solanum tuberosum subsp. andigena). Los fungicidas Mancozeb y Bravo alcanzaron efectos significativos en la reducción de la Curva de Progreso de la Enfermedad (incidencia y severidad) causada por S. lycopersici. Los modelos que mejor describen la curva de progreso de la enfermedad en ambas variedades son el de Gompertz y Logístico. Sin embargo, las formas linearizadas (LN) muestran tasas de infección similares y bajas, pero, se pueden considerar que muestran a una enfermedad destructiva. El efecto en la reducción de rendimiento por S. lycopersici alcanzó a 42,3 % para la variedad Waych´a y 51,5% para la variedad Imilla Negra.Fecha de aceptación: 4 de marzo, 2014
The basin of Lake Titicaca is a faba bean-producing microregion of Bolivia where the crop is destined for export. The most commonly cultivated ecotypes "Gigante de Copacabana" and "Usnayo" are affected by diseases that can cause production losses. The aims of the present work were to identify the causal agents of leaf spot affecting these ecotypes, to record disease intensity levels, and to estimate their effect on production. In 2004 and 2005, leaflet, stem and pod samples were taken from faba bean plants with leaf spot growing in the Lake Titicaca area, and from plants in an experimental plot established to determine the effect of five different treatments on production and disease intensity: T 1 = Control; T 2 = seed treatment with Trichoderma sp. + alternate foliar spraying with benomyl and mancozeb; T 3 = seed treatment with fludioxanil/metalaxyl M + alternate foliar spraying with benomyl and mancozeb; T 4 = foliar spraying with Trichoderma sp.; T 5 = alternate foliar spraying with cymoxanyl and mancozeb-chlorothalonil. Microscopic analysis of the samples revealed the presence of new fungal pathogens for faba beans in Bolivia (Cladosporium sp., and Lepthosphaerulina sp.) as well as emerging fungal pathogens (Botrytis cinerea, B. fabae, Ascochyta fabae, Alternaria sp. and Cercospora sp.). None of the treatments affected the disease progression curve (DPC) for incidence, although effects were seen with respect to disease severity. The seed + foliar treatments (T 2 and T 3 ) were more effective at controlling disease than leaf treatments on their own (T 4 and T 5 ). Modelling analysis showed faba bean leaf spot disease to be moderately destructive. Compared to chemical treatments, biocontrol with Trichoderma spp. preliminary was found to provide good control of the disease. Losses due to leaf spot disease of 36% were recorded, and a strong correlation detected between yield and disease severity.
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