The PCR results obtained for M. nivale var. nivale and var. majus were analysed in the same way as those for F. culmorum (Fig. 2b,c and d). When compared with the surrounding subplots, the frequency of M. nivale var. nivale and var. majus detection was relatively low in samples from the inoculated subplot (subplot 8), which had a high incidence of F. culmorum infection. This was particularly evident in rachis samples (Fig. 2d). M. nivale var. majus was detected in none of the glume components, and in only 8% of grain and 15% of rachis components of samples from this subplot. Similarly, M. nivale var. nivale was detected in none of the glume or rachis components and in only 8% of grain components of the samples. Subplot 9 also had a high incidence of F. culmorum infection but M. nivale var. nivale was not detected in any of the samples (Fig. 2b, c and d); var. majus was not detected in the glume components although it occurred in the grain, rachis or both components of 25% of the samples. PCR analysis revealed that there was a particularly high incidence of these pathogens in the 13 samples from subplot 7, 69% of samples being infected by M. nivale var. nivale and 92% of samples infected with var. majus. The pathogen was detected predominantly in the rachis components.
PCR analysis detected M. nivale var. nivale in 33, 25, 0, 0, 56, and 62% of the samples from subplots 1–6, respectively, while var. majus occurred in 66, 25, 50, 71, 33 and 77%, respectively. Again, both pathogens were found predominantly in the rachis components, often of the same sample, and as shown earlier, PCR analysis did not detect F. culmorum in any of these samples, many of which had low to moderate disease scores. M. nivale var. nivale was detected in 8, 11, 29, 0, 25 and 0% of samples from subplots 10–15, respectively, and var. majus in 23, 66, 86, 50, 50 and 66%. M. nivale var. nivale was found predominantly in the rachis component of these infected samples, often in conjunction with var. majus. M. nivale var. majus was often detected in the corresponding glume and rachis components of samples from subplots 10–15. Of the total of 21 M. nivale var. majus-infected samples from subplots 10–15, 63% were also infected by F. culmorum, and both pathogens were detected in the rachis component of 13 of the 14 co-infected samples. None of the five M. nivale var. nivale-infected samples from subplots 10–15 was infected by F. culmorum. Most M. nivale var. nivale and/or var. majus-infected plants from subplots 10–15 had been given low to moderate disease scores, although in a few cases no FEB symptoms had been seen (samples 97, 106 and 107 from subplots 11, 12 and 12, respectively). M. nivale was also detected in some samples from subplots 10–15 for which disease scores were relatively high, with var. majus in samples 96, 99, 103, 116, 120 (subplots 11, 11, 11, 13 and 14, respectively) and var. nivale in sample 120 (subplot 14). M. nivale var. majus and var. nivale PCR analysis for some of these samples is shown in Fig. 3(b). M. nivale var. majus was detected in the rachis of samples 96 and 99, which were also infected by F. culmorum (Fig. 3a), and which had disease scores of 68 and 100%, respectively. M. nivale var. majus was detected in the grain, glume and rachis component of sample 116 and 120, and in the rachis component of sample 103, while var. nivale was detected in the glume component of sample 120. F. culmorum was not detected in these samples, which had disease scores of 75, 84 and 55%, respectively. PCR analysis showed that var. majus was the predominant M. nivale subspecies within the field plot, with 64% of M. nivale-infected ears showing var. majus and 36% var. nivale. Since both M. nivale var. majus and var. nivale occurred on symptomatic and asymptomatic wheat ears, neither pathogen served to increase the correlation coefficient between visual disease assessment and PCR-based assays (Table 3). In tests of the association between pathogens (Everitt, 1986), the only significant association found was between F. culmorum and M. nivale (P < 0.01), there being an excess of samples where only one of the pathogens was present, i.e. F. culmorum or M. nivale var. majus/var. nivale.