Combining ability and gene action controlling rust resistance in groundnut (Arachis hypogaea L.)

Groundnut rust caused by Puccinia arachidis Speg. is a major cause of yield and quality losses in groundnut (Arachis hypogaea L.) in the warm-humid tropics including Tanzania. Breeding and deployment of rust resistant cultivars with farmer-preferred attributes will bolster groundnut production and productivity. The objective of this study was to determine the combining ability effects and gene action controlling rust resistance in groundnut genotypes for breeding. Twelve selected and complementary parental lines were crossed in a diallel design, to develop F1 progenies, which were advanced to the F2 for individual plant selection. Thirty-three successful partial crosses and the 12 parents were field evaluated using a 5 × 9 alpha lattice designs with two replications over two seasons in Tanzania. The tested genotypes exhibited significant (P < 0.05) variation for rust resistance, yield and yield-related traits. There existed significant (P < 0.05) difference on the general combining ability (GCA) effect of parents and the specific combining ability (SCA) effect of progeny for the assessed traits indicating that both additive and non-additive gene effects conditioned trait inheritance. The Bakers’ ratios indicated that the non-additive gene effects predominantly controlling rust resistance and yield components. This suggested that transgressive segregants could be selected for improved rust resistance and yield gains in the advanced pure line generations. Genotypes ICGV-SM 05570 and ICGV-SM 15567 were the best general combiners for rust resistance and grain yield. The crosses ICGV-SM 16589 × Narinut and ICGV-SM 15557 × ICGV-SM 15559 were identified as the best specific combiners for rust resistance with moderate yield levels and medium maturity. Genotypes with desirable GCA or SCA effects were selected for further breeding.

Breeding groundnut for rust resistance: A review

Sustainable groundnut production can be realised through development and adoption of high yielding cultivars possessing durable rust resistance. Integrating conventional breeding with genomic tools in identifying candidate rust resistance genes, and introgressing the genes into adapted elite germplasm, with the aid of molecular makers, could enhance breeding for rust resistance. This review highlights breeding approaches for groundnut rust resistance, with emphasis on integrating conventional breeding with marker-assisted selection. The life cycle, symptoms and epidemiology of the pathogen are also discussed to understand the host-pathogen interaction and guide groundnut rust resistance breeding

Purification, characterization, and antifungal activity of chitinase from Fusarium chlamydosporum, a mycoparasiteto groundnut rust, Puccinia arachidis

Chitinase (EC 3.2.1.14) was isolated from the culture filtrate of Fusarium chlamydosporum and purified by ion-exchange chromatography and gel filtration. The molecular mass of purified chitinase was 40 kDa as estimated by sodium dodecyl sulfate – polyacrylamide gel electrophoresis. Chitinase was optimally active at a pH of 5 and stable from pH 4 to 6 and up to 40°C. Among the metals and inhibitors tested, mercuric chloride completely inhibited the enzyme activity. The activity of chitinase was high on colloidal and pure chitin. The purified chitinase inhibited the germination of uredospores of Puccinia arachidis and also lysed the walls of uredospores and germ tubes. The results from these experiments indicated that chitinase of F. chlamydosporum plays an important role in the biocontrol of groundnut rust. Key words: Fusarium chlamydosporum, chitinase, purification, Puccinia arachidis, uredospores.

Biocontrol potential of rust of groundnut by Acremonium obclavatum

Acremonium obclavatum was frequently found associated with pustules of the rust fungus Puccinia arachidis on groundnut in Madras, India. Inoculation of A. obclavatum before, with, or after inoculation with P. arachidis reduced the number and size of uredosori both on intact and detached leaves of groundnut plants. Treatments with A. obclavatum resulted in reductions in number of pustules and uredospores, delay in maturity and opening of uredosori, and reduced viability of uredospores. The application of culture filtrates of A. obclavatum also reduced the number and size of pustules on intact and detached groundnut leaves. The potential use of A. obclavatum in biological control of groundnut rust is discussed. Key words: groundnut, Arachis hypogaea, groundnut rust, Puccinia arachidis, Acremonium obclavatum, biological control.