Resistance of Pinus taeda families under artificial inoculations with diverse fusiform rust pathogen populations and comparison with field trials

Controlled inoculations with 10 bulk inocula of Cronartium quercuum (Berk) Miyabe ex Shirai f.sp. fusiforme were carried out on open-pollinated progeny of 25 fast-growing Pinus taeda L. parents. The parents had a range of breeding values for resistance to fusiform rust in progeny field trials. There were highly significant differences among the halfsib families in response to inoculations, and these differences were very reproducible; the half-sib family-mean heritability of resistance to controlled inoculation was 0.97. All of the families that were susceptible in the field were susceptible in controlled inoculations, and most (12 of 17) of the field-resistant families were resistant in response to controlled inoculations. Significant pathogenic variability was observed among the different bulk inocula, although this accounted for only 1.9% of the total variation. Genetic differences among families within field-resistant or field-susceptible groups accounted for 13.7% of the total variation. The family by inocula interaction was highly significant, but a single field-resistant family contributed 44% of the total family by inocula interaction variance, and two other field-resistant families also showed significant interactions. Des tests d'inoculation controlee avec 10 sources d'inoculum de Cronartium quercuum (Berk) Miyabe ex Shirai f. sp. fusiforme ont ete effectues sur des descendances issues de pollinisation libre et provenant de 25 parents de Pinus taeda L. a croissance rapide. Les parents representaient une gamme de valeurs genetiques pour la resistance a la rouille fusiforme dans des tests de descendance sur le terrain. Il y avait des differences significatives parmi les descendances uniparentales en reaction aux inoculations et ces differences etaient tres reproductibles; l'heritabilite moyenne des descendances uniparentales pour la resistance aux inoculations controlees etait de 0,97. Toutes les familles qui etaient sensibles sur le terrain etaient egalement sensibles dans les essais d'inoculation controlee et la plupart (12 sur 17) de celles qui etaient resistantes sur le terrain etaient egalement resistantes dans les essais d'inoculation controlee. Une variation significative de la pathogenicite a ete observee parmi les sources d'inoculum bien que cela ne representait que 1,9 % de la variation totale. Les differences genetiques entre les familles parmi les groupes de familles resistantes ou sensibles sur le terrain representaient 13,6 % de la variation totale. L'interaction famille x source d'inoculum etait tres significative mais une famille contribuait a elle seule 44 % de la variation de l'interaction famille x source d'inoculum qui etait egalement significative chez deux autres familles resistantes sur le terrain. [Traduit par la Redaction]
Introduction Fusiform rust disease, caused by Cronartium quercuum (Berk) Miyabe ex Shirai f.sp. fusiforme (Cqf), is manifested by swollen regions called galls on stems or branches of pines, and is [...]