Resistance to Aspergillus flavus and A. parasiticus in almond advanced selections and cultivars and its interaction with the aflatoxins biocontrol strategy

Aflatoxin contamination of almond kernels, caused by Aspergillus flavus and A. parasiticus, is a severe concern for growers due to its high toxicity. In California, the global leader of almond production, aflatoxin can be managed by applying the biological control strain AF36 of A. flavus and selecting resistant cultivars. Here, we classified the almond genotypes by K-Means cluster analysis into three groups [Susceptible (S), Moderately Susceptible (MS), or Resistant (R)] based on aflatoxin content of inoculated kernels. The protective effects of the shell and seedcoat in preventing aflatoxin contamination were also examined. The presence of intact shells reduced aflatoxin contamination over 100-fold. The seedcoat provided a layer of protection, but not complete. In kernel inoculation assays, none of the studied almond genotypes showed a total resistance to the pathogen. However, nine traditional cultivars and four advanced selections were classified as R. Because these advanced selections contained germplasm derived from peach, we compared the kernel resistance of three peach cultivars to that shown by kernels of a R (‘Sonora’) and a S (‘Carmel’) almond cultivar and five pistachio cultivars. Overall, peach kernels were significantly more resistant to the pathogen than almond kernels, which were more resistant than pistachio kernels. Finally, we studied the combined effect of the cultivar resistance and the biocontrol strain AF36 in limiting aflatoxin contamination. For this, we co-inoculated almond kernels of R ‘Sonora’ and S ‘Carmel’ with AF36 72 h before or 48 h after inoculating with an aflatoxin-producing strain of A. flavus. The percentage of aflatoxin reduction by AF36 strain was greater in kernels of ‘Carmel’ kernels (98%) than in those of ‘Sonora’ (83%). Cultivar resistance also affected the kernel colonization by the biological control strain. AF36 strain limited aflatoxin contamination in almond kernels even when applied 48 h after the aflatoxin-producing strain. Our results show that biocontrol combined with the use of cultivars with resistance to aflatoxin contamination can result in a more robust protection strategy than the use of either practices in isolation.

Redcurrant genetic pool in selection for productivity

We report a study of 23 redcurrant cultivars of different genetic and geographical origin from the All-Russian Horticultural Institute for Breeding, Agrotechnology and Nursery’s genetic repository under the conditions of Moscow Region. The cultivar productivity was evaluated against the most important criteria of brush length, number of flowers and inception under contrasting weather conditions. A high cultivar resistance was registered to winter-born injuries and phytopathogens, including powdery mildew (Sphaerotheca morsuvae (Schw.) Berk. et Curt.), Septoria leaf spot (Septoria ribis Desm.) and anthracnose (Pseudopeziza ribis Kleb.). The established productivity under satisfactory weather conditions in growing season ranges from 1.75 (Kaskad) to 3.5 kg berries per bush (Serpantin, Yarkaya, Zametnaya), in most samples averaging to medium values of 2.7-3.0 kg. The inception rate was highest to exceed 60 % in Niva, Asya, Marmeladnitsa, Rote Spatleze, Serpantin, Yarkaya and Zametnaya. The most large-fruited with a 0.75 g average berry weight were Zadunayskaya and Niva cultivars. Serpantin, Yarkaya and Zametnaya originated by the All-Russian Horticultural Institute for Breeding, Agrotechnology and Nursery are recommended in selection for productivity for total marketing value, A concise cultivar morphobiological profile, origin, ripening period, chemical fruit composition, vigour and growth descriptions are provided.

Isolate Virulence and Cultivar Response in the Winter Wheat: Pyrenophora tritici-repentis (Tan Spot) Pathosystem in Oklahoma

Prevalence of tan spot of wheat caused by the fungus Pyrenophora tritici-repentis has become more prevalent in Oklahoma as no-till cultivation in wheat has increased. Hence, developing wheat varieties resistant to tan spot has been emphasized, and selecting pathogen isolates to screen for resistance to this disease is critical. Twelve isolates of P. tritici-repentis were used to inoculate 11 wheat cultivars in a greenhouse study in splitplot experiments. Virulence of isolates and cultivar resistance were measured in percent leaf area infection for all possible isolate x cultivar interactions. Isolates differed significantly (P < 0.01) in virulence on wheat cultivars, and cultivars differed significantly in disease reaction to isolates. Increased virulence of isolates detected increased variability in cultivar response (percent leaf area infection) (r = 0.56, P < 0.05) while increased susceptibility in cultivars detected increased variance in virulence of the isolates (r = 0.76, P < 0.01). A significant isolate × cultivar interaction indicated specificity between isolates and cultivars, however, cluster analysis indicated low to moderate physiological specialization. Similarity in wheat cultivars in response to pathogen isolates also was determined by cluster analysis. The use of diverse isolates of the fungus would facilitate evaluation of resistance in wheat cultivars to tan spot.

Two oat genotypes with different field resistance to Fusarium head blight respond similarly to the infection at spikelet level

Cultivar resistance is essential for the management of Fusarium head blight (FHB) disease in oat production. However, the breeders lack methods suitable for phenotyping disease resistance and resistance sources. In this paper we compared two oat genotypes, a rejected variety BOR31 and a landrace VIR7766, with four different traits that could reflect resistance to FHB in a greenhouse environment. Spray and point inoculations were used to inoculate Fusarium graminearum into flowering oat plants. When spray-inoculated, VIR7766 was significantly more resistant against the initial infection than BOR31, measured by the number of Fusarium-infected kernels and by DON accumulation. In the point-inoculated oats, the loss of fresh weight in the inoculated spikelet correlated well with the increasing F. graminearum biomass in the spikelet, measured six days after inoculation. However, no difference in the growth of the fungus was observed between the tested oat genotypes by point inoculation. We speculate that once the infection is established, the ability of the oat plant to resist the spread of the infection within a spikelet is low in the genotypes studied, although oat, in general, due to its panicle structure, is considered to have a high resistance against Fusarium infection.

Ranking Resistance of Buxus Cultivars to Boxwood Blight – an Integrated Analysis1

Boxwood (Buxus L. spp., Buxaceae) are popular woody landscape shrubs grown for their diverse forms and broad-leaved evergreen foliage, with an estimated $126 million economic impact in the U.S. alone. Boxwood plants grown in temperate zones worldwide are now threatened by a destructive blight disease caused by the ascomycete fungi, Calonectria pseudonaviculata and C. henricotiae. While the disease can be mitigated somewhat through cultural practices and fungicides, the most sustainable long-term solution is the development of disease-resistant boxwood cultivars. Hundreds of boxwood accessions from the National Boxwood Collection at the U.S. National Arboretum were screened for resistance using a lab-based, detached-leaf assay. Initial comparisons of our results with those of multiple other disease resistance assays found inconsistent ranking of cultivar resistance among studies. We used a meta-analysis approach on compiled data from six studies and were able to produce a consistent ordering of cultivars sorted by their susceptibility to boxwood blight, despite the diversity in materials and methods of the studies. Index words: Boxwood, Calonectria pseudonaviculata, Cylindrocladium buxicola, meta-analysis, plant breeding, resistance screening. Species used in this study: Buxus bodinieri H. Lev.; B. harlandii Hance; B. microphylla Seibold & Zucc.; B. sempervirens L.; B. sinica var. insularis (Nakai) M. Cheng; B. wallichiana Baill.; Calonectria pseudonaviculata (Crous, J.Z. Groenew. & C.F. Hill) L. Lombard M.J. Wingf. & Crous 2010.