The improvement of competitive saprophytic capabilities of Trichoderma species through the use of chemical mutagens

Abstract The antagonistic potential of Trichoderma strains was assayed by studying the effect of their culture filtrate on the radial growth of Sclerotium rolfsii, the causal agent of chickpea collar rot. Trichoderma harzianum-1432 (42.2%) and Trichoderma atroviride (40.3%) were found to be strong antagonists. To enhance their antagonistic potential, mutagenesis of these two selected strains was performed. Two mutants, Th-m1 and T. atroviride m1, were found to be more effective than their parent strains. The enzymatic activities of the selected parent and mutant strains were assayed, and although both mutants were found to have enhanced enzymatic activities compared to their respective parent strains, Th-m1 possessed the maximum cellulase (5.69 U/mL) and β-1,3-glucanase activity (61.9 U/mL). Th-m1 also showed high competitive saprophytic ability (CSA) among all of the selected parent and mutant strains, and during field experiments, Th-m1 was found to successfully possess enhanced disease control (82.9%).

Characterization of intrinsic variability of Mesorhizobium ciceri isolates of cultivated fields.

A large number of putative rhizobial isolates were obtained from the root nodules of various chickpea cultivars growing in agricultural research fields. Of these, thirty were selected and characterized for traits, such as, generation time, intrinsic azide resistance and several symbiotic characters.

Azide resistance in Rhizobium ciceri linked with superior symbiotic nitrogen fixation.

Isolated azide resistant (AzR) native R. ciceri strain 18-7 was resistant to sodium azide at 10 microg/ml. To find if nif-reiteration is responsible for azide resistance and linked to superior symbiotic nitrogen fixation, transposon (Tn5) induced azide sensitive mutants were generated. Using 4 kb nif-reiterated Sinorhizobium meliloti DNA, a clone C4 that complemented azide sensitivity was isolated by DNA hybridization from genomic library of chickpea Rhizobium strain Rcd301. EcoRI restriction mapping revealed the presence of 7 recognition sites with a total insert size of 19.17 kb. Restriction analysis of C4 clone and nif-reiterated DNA (pRK 290.7) with EcoRI and XhoI revealed similar banding pattern. Wild type strain 18-7, mutant M126 and complemented mutant M126(C4) were characterized for symbiotic properties (viz., acetylene reduction assay, total nitrogen content, nodule number and fresh and dry weight of the infected plants) and explanta nitrogenase activity. Our results suggested that azide resistance, nif-reiteration, and superior symbiotic effectiveness were interlinked with no correlation between ex-planta nitrogenase activity and azide resistance in R. ciceri.

Elaboración de un queso tipo cotija con base en una mezcla de leche y garbanzo (Cicer arietinum L) / Elaboration of cheese

The objetive of this work was to elaborate cotija type cheese prepared with whole milk and chickpea (Cicer arietinum L.), inoculated with S. Thermophilus and to compare its physicochemical, microbiological and sensorial characteristics with a commercial cheese. Two mixture were selected 70:30 and 80:20 (whole milk:chickpea paste). Both mixture were ground, pasteurized and inoculated with. S. Thermophilus, to develop taste and aroma. Two rennet concentrations (1:10,000 and 2:10,000), lactic acid and 50 per cent CaCl2 solution were used in both products. Results showed that cheese made with 70:30 mixture and 1:10,000 rennet concentration gave a weak curde and 12 per cent of total solids were lost; in the same way as 70:30 mixture and 2:10,000 rennet concentration. Nevertheless, cheese made with 80:20 mixture and 10,000 or 2:10,000 rennet concentration showed hard consistency of its curd. Addition of 10 per cent sodium chloride solution to he 80:20 mixture cheese, made better whey drain, and a cotija type cheese with similar sensory characteristics as a whole milk cheese, was obtained. Chemical and physical analysis of the extended cotija type cheese showed 14.3 +/- 0.42 and 15.5 +/- 0.21 g/100 g of protein and lipid content respectively. Microbiologically, the extended cotija type cheese is pathogenic microorganisms free for human consumption. Sensory evaluation of the chickpea extended cheese showed a 80 per cent acceptance while the acceptance of the whole milk commercial cheese was 90 per cent.