Host response to Pratylenchus thornei of a wheat line carrying the Cre2 gene for resistance to Heterodera avenae

The introgression wheat line H93-8 (bearer of the gene Cre2 for resistance to Heterodera avenae) was evaluated for response to Pratylenchus thornei an d H. avenae in a 5-month field experiment in comparison with its progenitor s and other wheat cultivars. Previously, the response of H93-8 to P. thorne i was compared to other T. aestivum cultivars under controlled conditions i n a 2 month laboratory assay. Line H93-8 was resistant to P. thornei under controlled conditions: after two months the nematode populations were less than half that in cv. Anza and H93-8 plants while they clearly increased in cvs Lores and Rinconada. Under field conditions, fewer H. avenae females w ere found in H93-8 and its wild donor Aegilops ventricosa than in the H10-1 5 wheat parent and the bridge species T. turgidum. No significant differenc es in the number of H. avenae indicated similarity between the resistance c onferred by Cre2 in line H93-8 and that regulated by Cre1 in cv. Lores. The parental line H10-15 hosted nearly half as many females as the susceptible control Capa, but as many as Rinconada. The variability observed in host r esponses to P. thornei when analysed under controlled conditions or in the field, makes it advisable to carry out both kinds of studies for the assess ment of resistant cultivars. Results in the field trial suggest that approx imately 5 months is the most secure time period to detect real differences in response to P. thornei due to penetration rates and reproduction of thes e nematodes depending on the line or variety. During the first 2.5 months, the population of P. thornei increased quickly in H93-8 but, at ear emergen ce, this line hosted similar numbers to its parents, Ae. ventricosa and H10 -15. T. turgidum was clearly the most susceptible host in the field to P. t hornei. The controls Rinconada and Lores were the least susceptible among t he plants tested in the field but, at the end of the experiment, they were significantly different only from T. turgidum. So, it was possible to detec t a differential host response or different levels of susceptibility, but n one of the tested cultivars or wheat lines was clearly resistant to P. thor nei under field conditions. Finally, a negative correlation between H. aven ae and P. thornei populations was detected in the field after 5 months only on cv. Lores.