Location: Crops Pathology and Genetics Research
2013 Annual Report
Objective 3. The investigators will work collaboratively to prepare annual analyses and summaries of the assessments described above (Objectives 1, 2). The information will be prepared and submitted by the investigators for inclusion on the PAW-MBA website and for presentation in county-based UC Extension meetings and newsletters. Field demonstrations will be held for selected trials, as appropriate. The investigators will collaborate with UC Farm Advisors in outreach efforts designed to foster awareness and optimal management of the emerging pathogens.
Ten cultivars and 26 breeding lines (= 36 genotypes) were tested for susceptibility to Fusarium wilt by immersing roots of runner plants in an aqueous suspension of 5 x 106 pathogen spores per ml. Of the cultivars tested, Monterey and Benicia were the most severely affected by Fusarium wilt, with resistance scores of 2.5 and 2.9, respectively (on 1-5 scale with 1 corresponding to a plant killed by Fusarium wilt and 5 corresponding to a plant with no symptoms of disease). As observed in previous tests, San Andreas and Portola were highly resistant, and both had scores of 5.0, which means that plants remained disease-free throughout the season. Ventana has appeared resistant in previous tests but in the 2013 test this cultivar had an average resistance score of 3.6, indicating that some damage resulted from the inoculations. Among breeding lines evaluated, scores ranged from 1.1 to 5.0, with an overall mean of 3.9. Sixty-two percent of breeding lines had resistance scores of 4.3 or higher.
Experiments were conducted to test the effects of the fungicide Topsin M (Cerexagri-Nisso LLC), and the biological products, Serenade Soil (Bayer) and Tenet (SipcamAdvan) on development of Fusarium wilt. All three products were tested at three inoculum levels (0, 10,000 and 25,000 colony forming units of F. oxysporum f. sp. fragariae per gram of potting mix), and two pH levels (pH 6 and.
Nine cultivars and three breeding lines were tested for susceptibility to disease caused by Macrophomina phaseolina. Plants were inoculated by dipping roots in a suspension of sclerotia prepared by blending fully colonized plated of potato dextrose agar in sterile water. The results revealed significant differences in susceptibility among the genotypes that were tested. A range in resistance scores of 2.0 to 4.5 resulted, implying that variation in susceptibility exists with the UC breeding population. We can now use this procedure to determine if the variation that we have observed is heritable and if it corresponds to similar variation in susceptibility under field conditions. A trial with an expanded set of genotypes is under way this year and results to date are consistent with last year’s findings. Our first attempt to assess the host range of Macrophomina phaseolina isolates from strawberry failed to document the susceptibility of other crops regarded as hosts to this pathogen. This could be an indication that the strawberry pathogen shows some degree of host-specificity, which could mean that rotations with these crops will not increase the risk of disease to a strawberry crop that follows in the same field. However, it is also possible that the inoculation method we used and/or the conditions under which plants were maintained were not conducive to disease development on the crops being tested. One factor that may be important is stress. Charcoal rot on many crops is closely associated with environmental stress, such as a lack of water. With this in mind, we are re-testing the same crops while subjecting them to stress induced by high temperature and by withholding water.