Dustin E. MacLean

An extensive survey conducted in the Saïss plain of Morocco during the 2017–2018 growing season revealed that 35 out of 50 apple and pear orchards were infested with a pathogen that causes the decline disease. Morphological and phylogenetic tree analyses using the cox II gene allowed us to identify the pathogen as Phytopythium vexans. Interestingly, no Phytophthora and Pythium species were isolated. The occurrence and prevalence of the disease varied between locations; the most infested locations were Meknes (100%), Imouzzer (83%), and Sefrou (80%). To fulfill Koch’s postulate, a greenhouse pathogenicity test was performed on the stem and collar of one-year-old healthy seedlings of apple rootstock M115. Symptoms similar to those observed in the field were reproduced in less than 4 months post-inoculation with root rot disease severity ranging from 70 to 100%. The survey results evidenced that apple rootstocks, soil type, and irrigation procedure may contribute significantly to the occurrence of the disease. The disease was most prevalent in drip water irrigation and sandy-clay soil on wild apple rootstock. Accordingly, a rational drip advanced watering system and good sanitation practices could eliminate water stagnation and help prevent the onset of this disease. It was concluded that Pp. vexans occurrence may be strongly influenced by irrigation mode and type of soil. Therefore, the obtained findings of this study could help to better understand the recurrence of this disease and to develop a reliable integrated strategy for its management.

The effects of applied nitrate on symbiotic nitrogen fixation in legumes are complex. Both inhibition and promotion of nodulation by nitrate have been observed in a dose‐dependent manner. The objectives of this study were to determine the effects of nitrate at different concentrations on root nodulation in different genotypes in common bean (Phaseolus vulgaris). Six genotypes were inoculated with the same rhizobial strain and grown hydroponically in growth pouches in a growth chamber and exposed to six nitrate concentrations, including 0, 2.5, 5, 10, 15, and 20 mM for 4 weeks. The tested genotypes included three recombinant inbred lines (RILs, 25, 46, and 70) that differed in their responses to nitrogen (based on observations of one field growing season), their parents (Mist and Sanilac—registered varieties), which are different in N‐fixing abilities, and one nonnodulating mutant (R99). Our results showed that small amounts of nitrate (2.5 and 5 mM) promoted nodule formation and increased nodule biomass, compared with plants in the 0 nitrate control treatment. In contrast, nitrate concentrations over 10 mM inhibited nodulation, resulting in reductions in nodule number and nodule biomass. Nodulation was completely inhibited by 15‐mM nitrate in all the genotypes. Regression analyses indicated that 5‐mM nitrate is the optimum concentration for promoting nodulation as measured by the total number of nodules formed, the number of effective nodules formed, and the nodule biomass formed. In contrast, nitrogen fixation was inhibited by all levels of nitrate. No genotypic differences were observed in nodulation among the three RILs and their parental cultivars, but all were significantly different than R99, a nonnodulating mutant.

Apple production in the Fes-Meknes region of Morocco is highly affected by pests and adverse weather conditions. A survey of apple farmers’ knowledge, perceptions and practices (KPP) in pest management and climate change was conducted in spring 2018 in two major apple-producing provinces of the region. Each farmer reported three insect pests and two diseases on average affecting their orchards. Pest management was performed by a combination of cultural and chemical methods. All farmers used dormant chemical sprays. About 60% of the respondents adopted pest surveillance based on visual inspection and 41.9% chose their pesticides on the basis of the information received from pesticide sellers. An average of 20 treatments per year was applied in each orchard. Regression analysis showed that neither the age of apple trees nor the number of pesticide applications influenced yield. Adverse weather conditions affected all apple plantations and the most frequent problems perceived were frosts, hailstorms, hot winds and water shortage. Of the orchards reported, 51.3% were protected with anti-hail nets. In order to reduce the rate of pesticide applications, better information on integrated pest management is required. Introduction of organic farming is necessary as 40.5% of the farmers agreed to convert to this practice in the future provided that market facilitation is established.

Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is one of the most destructive leaf spot diseases of wheat in Canada. Several races of the fungus are known to occur. Wheat growers have adopted fungicides to manage tan spot; however, intensive spraying may lead to development of reduced sensitivity to fungicides in the pathogen. In this study, 62 Ptr isolates were collected from across Saskatchewan and Alberta and characterized to race on a wheat differential set, with confirmation of race designations by polymerase chain reaction. This same set of isolates, and 27 isolates from an earlier study, were also evaluated for sensitivity to propiconazole and pyraclostrobin fungicides by determining the effective concentration of each needed to inhibit radial growth and conidiospore germination by 50%. Races 1 and 2 were predominant in western Canada, with 57% of isolates classified as race 1 and 40% as race 2. In Alberta, race 1 was most common (76%), while in Saskatchewan, it was race 2 (57%). Two of 26 isolates were classified as race 3, which was detected only in Saskatchewan in 2013. There was no evidence of reduced sensitivity of either fungicide in the Ptr isolates examined. This study provides a baseline for Ptr sensitivity to propiconazole and pyraclostrobin to which future collections of the pathogen may be compared.