Fusarium head blight of wheat: evaluation of morphological characters associated with desease resistance.

The most frequent pathogenic species producing head blight of wheat (Triticum aestivum L.) isolated in Argentina is Fusarium graminearum Schwabe. The fungus invades anthers, or may penetrate directly or by natural openings. Then, colonizes the rachis and the other spikelets. The main resistance mechanisms described are: to penetration (Type I), and to the spread (Type II).Previous studies have proposed morphological characteristics as associated with resistance Type I. We propose four morphological characters as associated to resistance or susceptibility.Spikes at heading and flowering stages of the susceptible cultivar PROINTA Oasis and the resistant Sumai 3, were inoculated and assesed at six times post inoculation. Disease severity was calculated, and the following morphological characters were measured: opening angle of anthecia, angle between lemma 1 and glume 1, rachilla and rachis lengths. Differences among these characters in each cultivar and between cultivars were evaluated, and were compared with the severity values.In both cultivars, the characters were constants over the time. The opening angle of anthecia was bigger at flowering than at heading and could be related with the increased severity in the resistant at that stage compared with the susceptible cultivar. The exposed lemma area was smaller at heading than at flowering in both cultivars which could represent the entry for the pathogen at the first stage. On the other hand, the rachilla and the rachis lengths were bigger in the resistant than the susceptible cultivar, and the severity was the opposite, which support the existence of a kind of resistance type II in the resistant cultivar.

Keywords: wheat, Fusarium head blight, resistance, morphological characters.