Wheat In France Research Articles

New Cases of Negative Cross-resistance between Fungicides, Including Sterol Biosynthesis Inhibitors

A survey of fungicide resistance in Mycosphaerella graminicola and Tapesia acuformis, two major pathogens of winter wheat in France, respectively responsible for speckled leaf blotch and eyespot, led to the characterization of two types of resistant strains to sterol 14α-demethylation inhibitors (DMIs). Most of the strains of M. graminicola collected in France in 1997–1998 were resistant to all DMIs, and only in a few strains was the resistance to several triazoles associated with increased susceptibility to pyrimidine derivatives (i.e., fenarimol, nuarimol) and triflumizole. On the other hand, in T. acuformis the most prevalent strains were those which exhibited negative-cross resistance between DMIs. In both fungi such a phenomenon could be related to changes in cytochrome P450 sterol 14α-demethylase, the target site of these fungicides. For Botryotinia fuckeliana, the causal agent of grey mould, the extensive monitoring conducted in French vineyards before the marketing of fenhexamid revealed the presence of highly resistant strains to this promising botryticide (only in tests involving mycelial growth measurements). Negative cross-resistance to edifenphos and several sterol biosynthesis inhibitors, such as prochloraz and fenpropimorph, was observed in fenhexamid resistant strains. Synergism of the antifungal action of fenhexamid by cytochrome P450 inhibitors, such as the DMI fungicides, was only recorded in fenhexamid resistant strains. These data and those previously obtained with edifenphos resistant strains of Magnaporthe grisea (rice blast pathogen) suggest that in fenhexamid resistant strains of B. fuckeliana the same cytochrome P450 monooxygenase could be involved in detoxification of fenhexamid and activation of edifenphos.

Protein evolution in dynamically managed populations of wheat: adaptive responses to macro-environmental conditions

Dynamic management of genetic resources aims to conserve genetic variability between different populations evolving in contrasting environments. It is thus of importance to determine whether differences appearing between populations are stochastic or if they come about from adaptation. Two-dimensional electrophoresis (2DE) was used to study genetic differentiation of 11 wheat populations evolving since 1984 in a multi-site network covering the major cultivation area of wheat in France. Gels were scanned and protein-spot intensities were measured through image analysis. As it was not possible to assay each individual, populations were characterized using pooled extracts from several plants. In the first step, two parents among the 16 parental lines involved in the initial wheat composite-cross population were exhaustively studied to identify a set of polymorphic spots against which the entire set of evolved populations could be compared. This analysis confirmed the efficiency of gel image-processing to determine the composition of pooled extracts. Of the 48 spots used to investigate population differentiation, 15 showed significant differences at the P<0.05 level. Populations that evolved independently at the same location showed similar differentiation, even when their cultivation methods were different. These results suggest that natural selection acted strongly on the evolution of the populations, and that responses to selection were determined primarily by macro-environmental conditions.

Influence of cropping system on foot rot of winter wheat in France

Wheat was assessed for foot rot and the responsible species ( Microdochium nivale, Fusarium spp.) identified at key stages on three different field trials: (a) the first comprised plots cultivated with cereals for a variable number of years after four years of non-cereals; (b) on the second, wheat was grown on compacted and uncompacted soil structure; (c) the third studied the effects of five wheat management techniques (sowing date and density, nitrogen fertilizer dose and form, removal/burial of cereal straw) on various sites. Microdochium nivale (which was predominant at early stages) and Fusarium spp. (which was predominant at later stages) were shown to behave very differently: the former was increased and the latter decreased where wheat was a previous crop, whereas foot rot as a whole was not affected by crop succession. Uncompacted vs compacted soil only increased foot rot at an early stage when M. nivale was predominant. Early sowing and high plant density (giving rise to low tillering) increased early foot rot and levels of M. nivale and decreased late foot rot and levels of Fusarium spp. A high vs low nitrogen rate and a low vs high ammonium content of the fertilizer increased foot rot; removal or burial of straw did not affect disease.

Climatic change and the growth and development of wheat in the UK and France

The crop simulation model AFRCWHEAT2 was used to predict the effect of climatic change on the yield and development of winter wheat in the UK and durum winter wheat in France. The model simulates crop responses to climatic variables dnd includes the effect of soil type on water and nitrogen availability to the crop. Crop simulations were made using individual, equilibrium 2 × CO2 general circulation model (GCM) scenarios and composite, time-dependent scenarios of future climatic conditions. AFRCWHEAT2 was most sensitive to changes in CO2 level and temperature, slightly less so to changes in the level of incoming radiation and least to reductions in amount of precipitation. The model calculated higher grain yields for composite time-dependent scenarios for all sites, but yields calculated from different GCM scenarios were more variable. There were no consistent changes in the coefficient of variation (CV) of yield. Management implications are that existing UK winter wheat varieties do not carry sufficient flexibility in their development to allow for adaptation to future climatic change and a more effective option would be to alter sowing date.Yield responses to climatic change cannot be predicted solely on the basis of average changes in climatic conditions but should take account of changes in the variability in the weather parameters to which growth is sensitive. A stochastic weather generator could serve this purpose.

Influence of Heterodera avenae on winter wheat in France: experiments with resistant and susceptible varieties

SummaryA succession of oat crops resistant or susceptible to Heterodera avenue produced plots lightly or moderately infested with the pest with little risk of interaction with other soil pathogens in succeeding cereal crops. Using these plots, the effects of the nematode on growth and yield of winter wheat were studied. The nematode affected the crop throughout its development, with a marked effect on yield. The effects of H. avenue are similar to those of water stress and are accentuated to a greater or lesser extent by climatic conditions. In the field the efficacy and durability of resistant genes incorporated in wheat and oats were checked. After four‐years' cultivation of oats (cv. Panema), no resistance‐breaking pathotypes were detected. Some advanced wheat lines with nematode resistance were also tolerant of nematode attack.