Breeding silage maize with brown-midrib genes. Feeding value and biochemical characteristics (1994)

The effects of the maize brown-midrib genes bm3 and bm1 on feeding value and agronomic traits were investigated by animal studies and biochemical approaches. When sheep were fed bm3 silage, an increase in digestibility was observed, equal to 2.4 points for digestibility of organic matter (DOM), and 8.1 points for digestibility of crude fiber (DCF). Phenotypic variation was reduced for all observed traits of bm3 hybrids. This allowed the assumption that the bm3 gene acted by levelling to a similar value of almost 74% DOM, quite independently of the original value of the normal counterpart. The bm1 hybrids were intermediate between normal and bm3 ones for DOM, DCF and intake, but the dry matter yield was not reduced for bm1 hybrids. From experiments with young bulls, feed efficiency of INRA260 bm1 was not significantly improved, compared with normal INRA260, but INRA260 bm3 was a lot more efficient. Despite its lower adverse effect on agronomic characteristics of hybrids, the bm1 allele did not appear to be of any interest in improving the silage maize feed efficiency. Variations for lignin content due to the bm3 gene was similar for the 3 hybrids studied, despite their variation for susceptibility to root and stalk lodging. Ratios and content of alkali-labile hydroxycinnamic acids behaved similarly for the 3 hybrids, with a low yield of para-coumaric acid. Structural studies of lignin, after thioacidolysis, strengthened the results pre- viously obtained, with a clear decrease of syringyl units, and the occurrence of the 5-hydroxyguaiacyl re- sidue. The lignin of bm3 genotypes also appeared as a more condensed polymer than that of the normal types. The decrease of lignin content was observed in only 1 bm1 hybrid and appeared the same between normal and bm1 hybrids as between normal and bm3 hybrids. The lower yield of para-coumaric acid, and the equal yield of ferulic acid after alkaline hydrolysis of bm1 material were in good agreement with previous work. After thioacidolysis, the release of monomeric syringyl units was similar between bm1 and bm3, about 30% of the normal counterpart. However, it was very different for guaiacyl units, with a large decrease of the release of these units from the bm1 hybrid. The ratio between syringyl and guaiacyl units was about 0.3 for bm3 hybrids and about 1.3 for the bm1 hybrid. The lignin of this bm1 hybrid appeared as a very condensed polymer compared with the normal type. A large variation for digestibility was also found among normal hybrids. However, inbred lines inducing high digestibility often included unfavorable agronomic traits, such as poor yield, susceptibility to lodging or stalk rot. Second or third cycle lines following pedigree breeding might combine all traits, even if stalk standability and stalk digestibility are partly antagonistic. This method may be considered as easier than the bm3 method, but at present, the 2 ways are probably complementary, and worth investigating for improving silage digestibility, and simultaneously increasing knowledge on silage maize digestibility. Zea mays = maize/feeding value / brown-midrib / bm1 / bm3 / lignin / hydroxycinnamic acids/thioacid olysis / syringyl / guaiacyl Rsum -Utilisation des gnes brown-midrib pour la slection du mas ensilage. Variabilit pour la valeur alimentaire et les caractristiques biochimiques. Les effets des gnes brown-midrib bm1 et bm3 sur la valeur alimentaire et les caractristiques agronomiques d'hybrides de mas ont t tudis partir d'essais sur animaux et de mesures de composition biochimique de la lignine. Sur moutons, les hybrides bm3 conduisent une amlioration moyenne de la digestibilit de la matire organique (DOM) * Correspondence and reprints. voisine de 2,4 et de celle de la cellulose brute (DCF) voisine de 8,1 points. La variabilit phnotypique est nettement rduite entre hybrides bm3, compare celle observe pour les quasi isogniques normaux, pour la quasi-totalit des caractres tudis. En particulier, il semble que la prsence du gne bm3 conduise augmenter la DOM des hybrides une valeur proche de 74%, quel que soit le niveau de digestibilit de l'hybride normal de dpart. Les hybrides bm1 se situent de faon intermdiaire entre les formes normales et bm3, sauf pour la productivit en biomasse qui est quivalente celle des normaux. Mais des essais de croissance compare de taurillons nourris avec des ensilages de mas INRA260, INRA260 bm1 et INRA260 bm3 montrent que la forme bm1 ne permet pas, contrairement la forme bm3, une amlioration notable des performances animales. La rduction de teneur en lignine a t semblable pour les 3 hybrides bm3 tudis, alors que ces hybrides prsentaient des diffrences importantes de sensibilit la verse ou la casse. Les teneurs et rapports entre acides hydroxycinnamiques librs aprs hydrolyse alcaline taient semblables chez les 3 hybrides, avec une libration faible d'acide para-coumarique caractristique des gnotypes bm3. La thioacydolyse confirme que la lignine des plantes bm3 est plus pauvre en units syringyl, avec, de plus, la prsence d'une unit 5-hydroxyguaiacyl. La lignine des plantes bm3 est un polymre plus condens que la lignine des plantes normales. Observe partir d'un seul hybride bm1, la diminution de la teneur en lignine a t semblable chez les plantes bm1 et bm3. Aprs thioacidolyse, la libration d'units syringyl tait quivalente entre bm1 et bm3. Mais la libration d'unit guaiacyl tait beaucoup plus faible pour la lignine des plantes bm 1, avec des rapports syringyl/guaiacyl voisins de 0,3 pour les bm3 et de 1,3 pour les bm1. La lignine des plantes bm1 est galement un polymre hautement condens. Une variabilit importante pour la DOM et la DCF existe aussi entre hybrides normaux. Toutefois, les hybrides les plus digestibles prsentent en gnral des dfauts agronomiques importants, qu'il sera sans doute possible de corriger au niveau de lignes de second ou troisime cycle. Actuellement, on peut considrer que les voies normales et bm3 sont deux approches complmentaires de l'amlioration et de la comprhension de la digestibilit du mas ensilage.