Strawberry (Fragaria x ananassa Duch.) is a nonclimateric fruit characterized by a short postharvest life, often estimated in less than 5 days. It is very prone to rapid dehydration, physiological disorders, bruising and other mechanical injuries, and to infections caused by several pathogens that can rapidly reduce quality of ripe fruits. These factors hinder to achieve export market and have limited strawberry production in Chile. Effect of boscalid on AbstractIn Chile, gray mold (Botrytis cinerea) and leak (Rhizopus stolonifer) are the major storage diseases of strawberry (Fragaria x ananassa Duch.) that considerably reduce yields and quality, limiting its international commercialization. The effect of preharvest fungicide treatments and postharvest treatments against storage decays was studied. Based on the results obtained, the incidence of B. cinerea and R. stolonifer was significantly lower on 'Camarosa' strawberry fruits treated with boscalid or boscalid + pyraclostrobin between blossom and harvest. Similarly, incidence of B. cinerea and R. stolonifer significantly decreased at 5ºC and 20ºC after immersion treatments with boscalid (600 to 700 mg L -1 ) or cyprodinil + fludioxonil (371 + 250 mg L -1 ). These postharvest treatments provided 5 and 15 days protection against these molds when strawberry fruits were stored at 20ºC and 5ºC, respectively. Fenhexamid (750 mg L -1 ) arrested B. cinerea, but it was ineffective against R. stolonifer. Variable results were obtained with iprodione (750 mg L -1 ). Fungicide treatments had no adverse effect on total soluble content, titrable acidity and firmness. Only boscalid + pyraclostrobin affected the external color of the treated fruits. In conclusion, fungicide treatments using new reduced-risk fungicides can be useful to extend strawberry shelf life for over a 15 day period. However, further research is needed to establish a commercial recommendation.Additional key words: boscalid, cyprodinil, fenhexamid, Fragaria, fungicides, pyraclostrobin. Resumen Efecto de boscalid sobre las podredumbres de la fresa en postcosecha causadas por Botrytis cinerea y Rhizopus stoloniferEn Chile, el moho gris (Botrytis cinerea) y el moho negro algodonoso (Rhizopus stolonifer) reducen los rendimientos y la calidad de la fresa (Fragaria x ananassa Duch.) en pre y postcosecha, limitando su comercialización internacional. En este trabajo se estudió la efectividad de tratamientos de campo y postcosecha sobre el desarrollo de podredumbres, vida útil y cualidades de la fresa conservada a 5ºC y 20ºC. De acuerdo con los resultados obtenidos, la incidencia de B. cinerea y R. stolonifer en postcosecha fue significativamente menor en fruta proveniente de fresas 'Camarosa' tratadas, entre floración y cosecha, con boscalid o boscalid + pyraclostrobin. Del mismo modo, fresas 'Camarosa' tratadas por inmersión en boscalid (600 a 700 mg L -1 ) o cyprodinil + fludioxonil (375 + 250 mg L -1 ), presentaron menor incidencia de B. cinerea y R. stolonifer tanto a 5ºC como a 20ºC. Este tratamiento proteg...

Resistance to the QoI fungicide (kresoxim-methyl) was detected in Venturia inaequalis (Cooke) Winter isolates from apple scab lesions collected from apple orchards in Chile after 5 to 6 years of commercial use of QoI fungicides. To reduce or prevent resistance development, QoI fungicides have been applied in blocks of two or three consecutive applications followed by an application of a fungicide with a different mode of action. However, the efficacy of kresoxim-methyl declined dramatically, providing almost no disease control in several orchards under high scab pressure in southern Chile, and resistance to the QoI fungicides was suspected. Conidia from at least five sporulating leaf scab lesions were collected from each of 10 and 14 orchards in 2003 and 2004, respectively. Fungicide sensitivity was determined by using a conidial germination test on potato dextrose agar acidified with 0.5 ml/liter of 95% lactic acid (APDA) containing kresoxim-methyl (Stroby 50 SC) at 0.0, 0.01, 0.1, and 1.0 μg/ml. The kresoxim-methyl concentration (0.01 μg/ml) has been used as a discriminatory dose in previous resistance studies (2). Germination was assessed for at least 100 conidia at each inhibitor concentration after 18 to 24 h of incubation at 20°C (1,2). Sensitivities were expressed as the percentage of germination relative to that on unamended APDA (1,2). These assays were repeated and all isolates with 50% effective dose (ED50) at >0.1 μg/ml were considered resistant. Isolates from eight of 10 and two of 14 orchards were resistant to kresoxim-methyl in 2003 and 2004, respectively. Relative germination varied from 42.4 to 100% for isolates from resistant orchards on 0.1 μg/ml of kresoxim-methyl, with eight isolates having ED50 at >0.1 μg/mL. Conidia from isolates obtained in 2003 also germinated on APDA amended with 1.0 μg/ml of kresoxim-methyl, with two isolates having ED50 at >1.0 μg/mL. Relative to the mean ED50 of 0.02 μg/ml of kresoxim-methyl determined for relative germination in North America baseline population of V. inaequalis (2), resistance factors for these Chilean isolates were estimated to range from 5 to 50. Conidia of resistant isolates continued to germinate in the presence of 0.1 μg/ml of kresoxim-methyl when 100 μg/ml of salicylhydroxamic acid was added to the amended APDA, suggesting that an alternative oxidase pathway was not responsible for the in vitro results obtained (2). A G143A target mutation has been detected in a V. inaequalis isolate from Chile, although no details concerning this finding were reported (Fungicide Resistance Action Committee, online publication, 2004 [ http://www.frac.info ]). The poor control of apple scab with QoI fungicides in Chilean orchards appears to be due to the development of resistant strains of V. inaequalis that occurred despite the limited use of these materials in blocks of two or three consecutive applications, as initially suggested for resistance management. Farmers have been advised to make only one application of QoI fungicide per year in a tank mixture with another type of fungicide or even to abandon the use of QoI fungicides for apple scab control. To our knowledge, this is the first report of a severe outbreak of apple scab due to the presence of populations of V. inaequalis resistant to QoI fungicides under commercial conditions in Chile. References: (1) R. B. Küng Färber et al. Pest Manage. Sci. 58:261, 2002. (2) G. Olaya and W. Köller. Plant Dis. 83:274, 1999.

‘WA 38’ is a new apple (Malus domestica Borkh.) cultivar, released by Washington State University (WSU) in 2017. An unknown disorder, ‘‘green spot’’ (GS), dark green halos in the epidermis, with necrotic, corky, and oxidated cortical tissue underneath the damaged epidermis, leads to unmarketable fruit and has become a threat to the adoption and profitability of ‘WA 38’, with young and mature orchards exhibiting up to 60% incidence in 2020. Given the apparent susceptibility of ‘WA 38’ to GS, this research investigated GS relation with nutrient levels in fruit. Research was carried out in 2018 and 2019 in a ‘WA 38’ apple block planted in 2013, on ‘Geneva 41’ (‘G.41’) and ‘M.9-Nic 29’ (‘M.9’) rootstocks. In both years, fruit number per tree, fruit weight, and fruit diameter were evaluated in 18 trees per treatment, from both rootstocks. From each tree, fruit were classified for presence or absence of GS, and subsequently analyzed for nutrient concentration in the peel and in the flesh, nutrient extraction, and total nutrient content, on an individual apple basis. Apples with GS had higher nitrogen (N) and magnesium (Mg) levels in the peel, regardless of year and rootstock. Apples grown on ‘G.41’ rootstock exhibited higher GS incidence and reduced crop load in both years; reduced size and fruit diameter were exhibited only in 2018. Fruit on ‘G.41’ had higher N, potassium (K), and Mg in the flesh and higher N and Mg in the peel, with lower levels of calcium (Ca) in the flesh and peel; however, only in 2018, with no differences in 2019. GS in ‘WA 38’ apples appears to be another Ca-related disorder in which excessive vigor, rootstock, and N and Mg excess are predisposing factors for its development.

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The phytoplasma Candidatus phytoplasma pruni (CPP), a causative agent of little cherry disease (LCD), has become an increasing problem for sweet cherry growers in Washington state, which is the largest producer of cherries in the USA. The control of LCD currently relies on the identification and removal of infected trees, which has proven to be difficult because of the prolonged asymptomatic, but still contagious state of the disease, and the lack of reliable and economical tests. Thus, the development of new approaches for early detection of LCD will be an important step in the successful control of this tree fruit disease. To identify potential microbial indicators of CPP infection we evaluated the bacterial and fungal communities in the roots of cherry trees from two different orchards that were: (i) infected with CPP and symptomatic; (ii) infected with CPP but remained asymptomatic; and (iii) healthy, non-CPP infected trees. We found significant variation in the microbiomes between the two cherry orchards, with the location being a stronger driving factor determining the fungal compared to the bacterial community. The fungal communities were less affected by the disease conditions compared to the bacterial microbiome. Overall, this study demonstrates feasibility of the microbiome approach for the early detection of LCD by CPP, but also demonstrates that more orchards need to be sampled as location was a stronger contributor to the microbiome of cherry tree roots than disease condition.