Late wilt (causal agent Harpophora maydis), with initial symptoms appearing around flowering, has become frequent in maize fields of the Iberian Peninsula. The geographical distribution of the pathogen in the main maize - growing areas in the South of Portugal and Spain was determined by prospecting 59 fields from 2009 to 2013. Among all the isolates of H. maydis identified, 14 isolates were molecularly confirmed by ITS amplification, and their pathogenic traits (i.e. aggressiveness) were analyzed by inoculation of the maize susceptible cultivar PR32W86 grown in pots under shade-house conditions for the whole growing season. One of the isolates was highly aggressive, causing intense symptoms as well as significant reductions in weight of both aboveground parts and roots. Moderately aggressive isolates caused significantly high disease values but not all of them were related to reductions in plant weight. The infection by H. maydis was monitored by measurements of canopy temperature and crop water stress index of maize. Canopy temperature was assessed in potted control plants and in plants inoculated with the most aggressive isolate in two experiments conducted outdoors in 2012 and 2013. Both indices responded to the presence of fungal infection in both years, which was detected up to 17 days before development of symptoms in the plants. This study shows the wide distribution of H. maydis in the Iberian Peninsula and highlights the importance of genetic resistance for controlling the pathogen in southern Europe. In addition, the thermal detection of the infection prior to symptom development might lead to useful applications of non-destructive pre-symptomatic disease diagnosis in controlling late wilt disease in maize.

Research partially supported by the Spanish National Research Council (CSIC) (PIE200940I120).

Peer reviewed