Ergosterol analyses of seed samples infected with Fusarium culmorum from 22 wheat genotypes differing in resistance to Fusarium head blight indicated that visual assessment of head blight levels from a field plot gives a reliable estimate of the amount of fungal biomass. The percentage of infected spikelets was a better indication of the amount of fungal biomass present than the percentage of infected heads. This suggests that Fusarium head blight resistance in this population is mainly based on resistance to colonization and that resistance to establishment of the initial infection plays only a minor role. Plants from a susceptible and a resistant breeding line were inoculated with F. culmorum at flowering time. Four weeks after inoculation heads were selected with Fusarium-infected spikelets levels ranging from 0 to 100%. At this time only low levels of ergosterol were detected in the kernels. Eight weeks after inoculation, ergosterol concentrations in chaff and kernels were significantly higher in the susceptible line compared with the resistant breeding line. At 4 and 8 weeks after inoculation the trichothecene deoxynivalenol content of chaff and kernels was also much higher in the susceptible line than in the resistant line. The Fusarium head blight resistant line possesses resistance to hyphal invasion. It appears that deoxynivalenol is transported from the chaff to the young kernel and the pathogen then colonizes the kernel. In the resistant line deoxynivalenol translocation from chaff to kernel was inhibited and little fungal colonization occurred. It is hypothesized that this is based on a membrane-based trichothecene tolerance. Key words: wheat, Fusarium, trichothecene, resistance, ergosterol, deoxynivalenol.

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Organic matter and cell wall degradation (OMD and CWD) are important quality traits of maize which may be estimated by in vitro assays using rumen fluid. However, these assays have some large disadvantages which stimulate research for alternative methods. The objective of this study was to evaluate the potential of the thermal analysis techniques, differential scanning calorimetry (DSC) and thermogravimetry (TG), to estimate OMD, CWD, and related forage quality traits of maize. For all DSC and TG properties distinguishable in DSC and TG thermograms, large variations existed among 25 maize samples. Multiple linear regression models including both DSC and TG variates could explain a major part of the variation of most forage quality traits. The relatively short analysis time, the high reproducibilty of measurements, and the high predictive potential as shown by the low standard error of prediction indicate that DSC and TG may be used to predict forage quality characteristics of maize. Keywords: Degradability; cell wall; maize; differential scanning calorimetry; thermogravimetry; multiple linear regression

Abstract:The stalk fraction of recombinant inbred lines of maize (RILs), harvested shortly before silage stage, was used to determine genetic variation for organic matter digestibility (OMD) and cell wall digestibility (CWD) as well as variation for fibre content (eg neutral (NDF) and acid detergent fibre (ADF)) and chemical composition (eg hemicellulose, cellulose, lignin, total phenolics and the phenolic acid esters: p-coumaric, ferulic and vanillic acid). OMD and CWD, as monitored in an in vitro incubation using rumen fluid, ranged between 64.6 and 80.7% and 44.9 and 63.0%, respectively. The fibre content varied from 460 to 675gkg-' dry matter (NDF) and from 258 to 405gkg-' dry matter (ADF). Generally, hemicellulose (HEM) was present in lower amounts in the cell wall than cellulose (CEL). Comparison of two subsets of the RILs with either a low or a high CWD demonstrated that the RILs with the low CWD contained higher concentrations of fibre and enhanced amounts of all cell wall constituents measured except for HEM and ferulic acid (Fa). The Fa content of the low CWD subset was lower and no significant subset difference was present for HEM. The correlations between two blocks in a field trial (repeatability) was high for all forage quality traits, except HEM, total phenolics (tPHEN), pcoumaric acid and vanillic acid. A close negative relationship existed between OMD and NDF, ADF, CEL and permanganate lignin (pLIG) showing absolute correlation coeffcients above r = 0.80. The association of CWD to these cell wall properties was either weak or moderate. In contrast to all other cell wall constituents, tPHEN correlated better to CWD than to OMD (r = -0.82 and -0.62, respectively). By means of multiple regression, a regression equation was generated for CWD and OMD using ASH, pLIG and tPHEN or ASH, NDF, pLIG and tPHEN, respectively, as explanatory variables. About 92% of the variation of OMD and 80% of the variation of CWD could be explained by these regression models with residual standard deviations of 1.37% and 2.19%, respectively.