ABSTRACT
Alfalfa (Medicago sativa) is the most cultivated fodder crop in Peru with 172,000 ha cultivated (MINAM 2019), and Arequipa is the top producing region with 40% of the national production in 2015 (Santamaría et al. 2016). In January-April 2019 (av. 20°C and 70% RH), most alfalfa fields in Majes-Pedregal, Arequipa were affected by an unidentified foliar disease. One of the fields was located at the farm of the Universidad Nacional de San Agustín de Arequipa (16°19'29.6" S, 72°12'59.9" W). Symptoms appeared as elliptical light brown spots witdark brown borders (Fig. S1a and b). The field (~60 × 60 m) was divided into ~30 × 12 m sections and two plants in each section were collected (20 plants total). Plants were digitized and the leaflet diseased area was calculated with ImageJ 1.53a, from which an incidence of 100% and a severity of 38.7 ± 4.4 % were estimated. Microscopical observations at the leaflet spots revealed consistently the presence of oblong multiseptated conidia (23.6-42.8 × 16.5-25.2 µm; av. 33.3 × 20.9 µm; n = 40) of the genus Stemphylium (Simmons 1969; Woudenberg et al. 2017) (Fig. S1c). We obtained 10 pure cultures by placing conidia from the spots directly onto potato dextrose agar medium with the aid of stereoscope and sterile forceps. Two isolates (UNSA-StemV01 and UNSA-StemV02) were incubated further until ascospore production at room temperature with no special light stimulus. After 45 days of growth, globose pseudothecia and ellipsoidal ascospores (25.4-38.7 × 11.2-16.6 µm; av. 31.9 × 13.7 µm; n = 30) formation occurred (Fig. S1d and e). We extracted the DNA from these two isolates using Wizard® Purification Kit (Promega Corp., Madison, WI) and sequenced the internal transcribed spacer 1 and 2 intervening 5.8S rDNA subunit (GenBank accessions: MT371236-37), and the glyceraldehyde-3-phosphate dehydrogenase (MT375513-14) and the calmodulin (MT375515-16) genes, highly resolutive markers to identify Stemphylium species, following Woudenberg et al. (2017). We retrieved sequence data available from 43 isolates of nine Stemphylium species (Han et al. 2019; Woudenberg et al. 2017), and built a mid-point rooted phylogeny with the three-loci concatenated data set (Fig. S2). We identified our isolates as S. vesicarium (Fig. S2). Koch's postulates were fulfilled by spray-inoculation with conidia from isolate UNSA-StemV01 suspended in sterile water (1×104 / mL) to two healthy 50-day old alfalfa plants growing on pots in the university greenhouse (av. 25°C and 70% RH). Two plants sprayed with sterile water without conidia served as control. Symptoms appeared after 21 days of inoculation, and when conidia were re-isolated, they were the same as originally obtained. No symptoms developed in the control plants. This confirmed that S. vesicarium is the causal agent of the alfalfa disease in Majes-Pedregal, identified as Stemphylium leaf spot. revious studies documented S. vesicarium on asparagus and onion in Peru (Castillo Valiente 2018; Vásquez Salas 2018; Vásquez Sangay 2013), but molecular characterization has only been applied to S. lycopersici from potatoes (Woudenberg et al. 2017). Stemphylium vesicarium has been documented in various crops, including alfalfa, and countries in Europe, North America, Africa, Asia and in Australia and New Zealand (Han et al. 2019; Woudenberg et al. 2017). This occurrence is the first report of S. vesicarium on alfalfa in Peru. The disease compromises the quality of this fodder crop, so actions need to be taken in Arequipa.
ABSTRACT
Little is known about the major issues leading to postharvest losses in Peru, which are estimated to be 15-27%. We surveyed 503 farmers from the lowlands and Andean regions of Arequipa to learn more about the major grains produced and issues encountered during drying and storage. Rice, common bean, and quinoa were the most grown crops in the lowlands while starchy maize was the most cultivated crop in the highlands. Most farmers (90%) dried their crops in-field directly on the ground, which exposes them to rodents, birds, and insect pests. The majority of farmers (92%) used subjective methods to assess grain moisture content. About 77% of farmers identified insects as a major challenge during storage but only 44% said they used preventive measures such as the application of insecticides. Among farmers who stored grain, the main reason was for household consumption (61%); while among those who did not store, the main reason was the need for immediate cash at harvest (75%). Farmers who experienced insect problems, who stored seed or grain for sale, who stored longer, or farmers from the lowlands were more likely to apply insecticides on their stored products. These findings provide an opportunity for researchers, development organizations, and government agencies to improve postharvest handling and storage in Arequipa by disseminating drying technologies, moisture assessment tools and hermetic storage solutions among farmers.
