INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE-INRA
Station d'Amélioration des Plantes, BP 35327, 35653 Le Rheu, France.
G. Doussinault, F. Dedryver, J. Jahier, D. Barloy, H. Muranty,
B. Rolland, and M. Trottet.
Rumba bread wheat, developed by Institut National de la Recherche Agronomique, was released in autumn 1999. Rumba is derived from the cross 'Fresco/R3-7//CW3547/Florin' made in 1987 at Le Rheu Plant Breeding Station. R3-7 is an INRA line issued from the cross 'VPM/Moisson//US(60)43/Prieur', and CW3547 is a line from PBI Cambridge from the cross 'TW275/Norman'.
Rumba has a winter growth habit with a high frost resistance and medium resistance to lodging and is medium early and short-strawed with an awnless spike. The cultivar is high yielding, especially in conditions with high disease development; its mean yield in official tests for registration was 108 % of the yield of the control varieties (the four varieties most widely grown in northern France). Rumba has a good quality for making French bread, but is susceptible to sprouting in the ear before harvest. Rumba has a good level of resistance to eyespot conferred by the gene Pch1 derived from Ae. ventricosa via VPM and R3-7 and resistant to leaf rust and powdery mildew and moderately resistant to Septoria leaf blotch and powdery mildew. Rumba has the gene cluster Yr17-Lr37-Sr38, but the resistance to yellow rust was overcome in 1998 by new pathotypes.
Rumba is a registered variety maintained by Agri-Obtentions, domaine de la Minière, BP 46, 78042 Guyancourt, France. Small samples of seeds for scientific purposes can be obtained from G. Doussinault.
RE9001 bread wheat developed by INRA was registered in autumn 1998 as hybrid parental line. The line is derived from a cross between INRA breeding lines. RE9001 has a winter growth habit, is medium late, and has very short straw and an awnless spike. With a good level of resistance to diseases, RE9001 has the genes Pch1 and Yr17-Lr37-Sr38 and has good potential to contribute resistance to disease to hybrids.
Our work with powdery mildew aims at better understanding adult-plant resistance in the field. Analysis at the seedling growth stage of the genes for specific resistance in the French varieties released in 1996 and 1997 showed that only seven genes are present: Pm2, Pm4b, Pm6, mli, ar, Pm8, and Pm3a. Three cultivars have four resistance genes, one cultivar has three genes, 13 cultivars have two genes, 12 have only one gene, and 11 lack any resistance genes to powdery mildew. All these genes, except Pm3a, frequently are overcome by the French populations of powdery mildew. Varieties with Pm3a are very infrequent in France.
Besides the genes effective at the two-leaf stage, other genes are expressed later, and their effect can be measured on vernalized plants at the five-leaf stage. Genotypes are infected with isolates that overcome the two-leaf stage resistance. Some varieties have a high level of resistance to some of these isolates, indicating that another system of resistance is initiated during vernalization.
Nevertheless, varieties without specific resistance genes or with defeated genes may express adult plant resistance. The study of vernalized seedlings can reveal an important part of adult plant resistance. Testing genotypes at these three growth stages allows better understanding of resistance of wheat to powdery mildew.
Pathotypes of yellow rust that can overcome the resistance gene Yr17 appeared in France in 1997, and a severe epidemic occurred in 1999. A molecular-marker study showed that about half of the varieties registered since 1996 have Yr17, but only a small number of these varieties have become very susceptible. The progenitor line VPM, in which the gene Yr17 was introduced from Ae. ventricosa, has been used widely in breeding programs, and many varieties have additional genes for resistance. The gene Lr37, which is linked to Yr17, is still efficient.
Aegilops peregrina accession 1 is the only known source of resistance in the Triticeae subtribe to the root-knot nematode, Meloidogyne naasi. Previous studies showed that this resistance was conditioned by the dominant gene Rkn-mn, which has been transferred into wheat by a translocation to chromosome 3B. Isoenzyme and RAPD markers were found, and the three closest, flanking RAPD markers were mapped at 0 cM, 0.8 cM, and 1.7 cM from the resistance gene.
High frequencies of off-types that result from an aneuploid condition cause problems with seed certification. About one-third of the leading French varieties were demonstrated to be affected by this phenomenon, the importance of which depends on the year. Although investigations have documented a few aneuploid conditions, more research is necessitated for better understanding the appearance of aneuploids. The seed sector shows concern about this situation and is the reason for a study initiated by INRA, CTPS (Technical Committee for Plant Breeding), and the seed companies. The goals of the study are to describe the phenomenon on both a phenotypic and a cytological basis and find environmental and genetic causes.
Among the wheat varieties released in the last 10 years, an increasing number are improved not only for yield potential, but for disease resistance as well. These new varieties with a high general level of resistance to diseases are not always grown widely by farmers, and, when they are, they often receive the same amount of fungicides as the more susceptible varieties. Changes in the price of grain in Europe and the agricultural policy of the European Commission have triggered the development of less costly and more environmentally friendly agricultural practices. To promote varieties resistant to disease, INRA, ITCF, and some seed companies decided to compare varieties cultivated with different input levels in a network of trials. The results will be analyzed not only for grain yield but for financial yield, cost of production of a unit of grain, and the effect on the environment.
Four husbandry levels are compared. Intensive cultivation is used most commonly by farmers, i.e., nitrogen supply adjusted for the yield attainable 5 years out of 10 in the field, growth regulators, and three fungicide treatments. Extensive cultivation includes a seeding rate reduced by 40 %, nitrogen reduced by 60 kg/ha, and no growth regulator or fungicide. Two intermediate levels also are in the trials. Five or six varieties are grown at the four husbandry levels according to the location. Herbicide is applied at all levels, because the effect on weed frequency has to be estimated in a crop rotation. Nine trials were conducted in 1999, and 13 are planned for 2000.
Conclusions are impossible from a 1-year trial, but the first results show that if the most intensive level generally gives the best grain yield, there is more variability for the financial yield. We observed important interactions among locations, varieties, and husbandry level. The extensive level is the most environmentally friendly but not always the best for the economics of the crop.