Abstract

QUIROZ, F.J et al. Impacto de las enfermedades foliares sobre variables fisiológicas determinantes del rendimiento del girasol ante diferentes situaciones de cultivo. RIA. Rev. investig. agropecu. [online]. 2018, vol.44, n.3, pp.333-343. ISSN 1669-2314.

Leaf spot by Alternaria (ALT) and black stem spot by Phoma (BS) are endemic leaf diseases of sunflower in Argentina. BS regularly reduced the yield of high potential sunflower of the south of Buenos Aires. Environmental variability between years and sowing date affect the occurrence of these diseases however the information about its effect is scarce. The objective of this work was to assess the occurrence and importance of leaf diseases on yield, number and weight of achenes, and oil content, in different environments (years and sowing dates) in the south of Buenos Aires, Argentina. Five experiments were performed at the field station of INTA Balcarce in the years 2003, 2005, 2007, 2008 and 2009 under field conditions and natural inoculation. Five hybrids, protected or not protected with a mixture of foliar fungicides, were evaluated. Three experiments included two sowing dates (early and late). Leaf area, incidence and severity of diseases, yield, number and weight of achenes, and oil content were measured. BS was the disease with the highest prevalence and incidence (19 to 81%). Less frequently, severe ALT (0.3 to 10%) and atypical black rust by Puccinia helianthi (BR, 0 to 23%) were observed in 2007. The higher rainfall and relative humidity observed at late sowing dates corresponded to an increase in incidence or severity of symptoms (> 70%), mainly of ALT. BS, ALT and BR decreased leaf area duration mainly in leaves of medium or higher strata, while fungicide protection reduced its effect. BS was the disease that was most associated with decreased weight and number of achenes. The oil content decreased in the control treatments in association with late sowing and the presence of ALT. The effect of foliar diseases on yield (11 to 17 %), the number and weight of achenes, and the oil content varied with experimental environment and in relation to the incidence of BS and the occurrence of severe epiphytes of BR and ALT. Application of foliar fungicides resulted in productive benefit.

Keywords : Leptosphaeria lindquistii; Alternaria helianthi; Helianthus annuus L; Leaf area; Leaf area duration; Fungal protection; Yield; Achenes weight; Achenes number.

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