STUDY OF SUITABLE CANDIDATE GENES INVOLVED IN RESISTANCE TO FUSARIUM GRAMINEARUM IN DURUM WHEAT

Wheat is one of the most important crop species world-wide, and is affected by several fungal diseases. In the cold and rainy European countries, one of the most damaging is the Fusarium head blight (FHB) caused by several species of Fusarium genus (F. graminearum, F. culmorum, F. avenaceum, F. poae), which leads to severe yield reduction and phytosanitary concerns due to the accumulation of mycotoxins harmful to humans and livestock. Host resistance is the primary control measure for FHB, thus the development of resistant varieties is one of the most attracting challenges in modern breeding projects. Unlike in bread wheat, only poor information is available on tetraploid species, so that advances in this field are strictly correlated to deciphering the genetic basis of Fusarium resistance. One of the hypothesis about tetraploid wheat vulnerability is that it may carry some susceptibility factors and/or resistance gene suppressors. The objective of the present work was to identify some genes which can be suitable “candidate” in the mechanism of resistance to FHB, and to assess their involvement by means of expression studies. We focused attention on genes encoding for enzymes involved in cell wall polysaccharides modification (the first physical hurdle to fungus penetration) or detoxification of mycotoxins (suggested virulence factors responsible for pathogenesis). In particular, we tested pme (pectin methylesterases) for the first category, and LTP-1 (Lipid Transfer Protein) for the second one. Expression analyses were carried out on spikes from susceptible and resistant durum wheat lines belonging to a segregant population obtained from crossing the hexaploid resistant line 02-5B318 and the susceptible durum variety Saragolla, harvested at different days after inoculation. For both pme and LTP-1, differences between the two parents were recorded in the late infection stages, when the genes expression level in the resistant 02-5B-318 was significantly higher than in the susceptible Saragolla. Moreover, while this cultivar showed a constant expression of the candidate genes during infection, gene expression was constantly increasing in the resistant parent. Differences in gene expression profile between the group of resistant and susceptible lines of the population, mirrored that between the two parents. This work seems to confirm the role of pmi and LTP as candidate resistance genes for FHB: in the resistant lines, LTP is overexpressed in order to restore the redox state of the cell altered by the fungus, thus inhibiting the synthesis and accumulation of mycotoxins. On the contrary, expression of pme seems to be downregulated in order to keep a high methylation degree of pectin, thus ensuring cell wall compactness as a physical barrier against fungal penetration. The role of pme in the resistance mechanism at the cell wall level was confirmed also by positive statistical correlations found between cell wall pectin methylation degree and resistance level (assessed as incidence and severity).