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Adoption of cover crops in arid agroecosystems has been slow due to concerns regarding limited water resources and possible soil moisture depletion. In irrigated organic systems, potential ecosystem services from cover crops also must be considered in light of the concerns for water conservation. A constructive balance could be achieved with fall-sown small grain cover crops; however, their impacts on irrigated organic systems are poorly understood. Our first objective was to determine the ability of fall-sown small grains [cereal rye (Secale cereale L), winter wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and oat (Avena sativa L.)] to suppress winter weeds in an irrigated, organic transition field in the southwestern USA. Small grains were planted following the legume sesbania (Sesbania exaltata (Raf.) Rydb. ex A.W. Hill) during Fall 2012 and Fall 2013. In Spring 2013 and 2014, weed densities and biomass were determined within each cover crop treatment and compared against unplanted controls. Results indicated that both barley and oat were effective in suppressing winter weeds. Our second objective was to compare weed suppression and soil moisture levels among seven barley varieties developed in the western United States. Barley varieties (‘Arivat’, ‘Hayes Beardless’, ‘P919’, ‘Robust’, ‘UC603’, ‘UC937’, ‘Washford Beardless’) were fall-sown in replicated strip plots in Fall 2016. Weed densities were measured in Spring 2017 and volumetric soil moisture near the soil surface (5.1 cm depth) was measured at time intervals beginning in December 2016 and ending in March 2017. With the exception of ‘UC937’, barley varieties caused marked reductions in weed density in comparison with the unplanted control. Soil moisture content for the unplanted control was consistently lower than soil moisture contents for barley plots. Barley variety did not influence volumetric soil moisture. During the 2017–2018 growing season, we re-examined three barley varieties considered most amenable to the cropping system requirements (‘Robust’, ‘UC603’, ‘P919’), and these varieties were again found to support few weeds (≤ 5.0 weeds m−2). We conclude that several organically certified barley varieties could fill the need for a ‘non-thirsty’ cover crop that suppresses winter weeds in irrigated organic systems in the southwestern United States.

‘Mexican June’ was a popular white, open-pollinated maize variety grown in the southwestern and southern USA. It was well adapted to both semi-arid and humid, hot environments and it was utilized for forage and grain. Its production waned with the maize hybrid revolution of the 1930s and 1940s—even though it was proven to outperform the new hybrids in hot, dry climates of the Southwest. The rising popularity of locally grown heirloom crops has increased interest in landrace varieties. There is also increasing focus on desert-adapted crop genetic resources as the need for more climate resilient crops is recognized. We tested the yield performance of six accessions of ‘Mexican June’ in comparison with organic certified commercial hybrids in southern New Mexico. We also documented several plant and ear traits to distinguish variation across the accessions. Several accessions yielded at or near commercial hybrid levels, attesting to the adaptation of ‘Mexican June’ to hot, semi-arid environments. This finding demonstrates that ‘Mexican June’ may prove useful in non-GMO production systems, and as a genetic resource for the improvement of abiotic stress tolerance in new, more resilient varieties. Variation in plant, ear, and kernel traits between accessions of ‘Mexican June’ was consistent with the hypothesis that there is not a single variety of ‘Mexican June’, but multiple varieties that form a complex.

Field production of organic fresh-market tomatoes in the U.S. Desert Southwest is desired by local producers and consumers. Tomato yield and fruit quality can be seriously impacted by heat stress (HS) and beet curly top virus (BCTV) infection of the main-season crop. We examined delayed planting of HS tolerant cultivars as a strategy for avoiding and mitigating these abiotic and biotic stressors. In 2016, seven putative HS tolerant cultivars, and one considered to be heat susceptible, were transplanted to the field in mid-summer to avoid peak populations of beet leafhopper (Circulifer tenellus), the vector of BCTV. In 2017, seven HS tolerant cultivars, one heat-susceptible, and two hot-set hybrid cultivars were transplanted in mid-summer. Fruit set was above 75% for most entries, including the heat-susceptible checks. Open-pollinated (OP) and hybrid cultivars exhibited a range of yields from 21.3 to 148.6 Mg/ha and fruit quality ratings from poor to excellent. The OP check ‘Super Sioux’ displayed consistently good yield and quality across years. The correlation between fruit set and yield was low (R2 = 0.29) and significant only at the 0.10 level (P

Maize has played a key role in the sustenance and cultural traditions of the inhabitants of the southwestern USA for many centuries. Blue maize is an important component of the diverse landraces still cultivated in the region but the degree to which they are related is unknown. This research was designed to ascertain the genotypic, morphological, and phenotypic diversity of six representative southwestern blue maize landraces. Their genotypic diversity was examined using tunable genotyping-by-sequencing (tGBS™). A total of 81,038 high quality SNPs were identified and obtained through tGBS. A total of 45 morphological and biochemical traits were evaluated at two locations in New Mexico. The varieties Los Lunas High and Flor del Rio were genetically less related with other southwestern landraces whereas diffusion between Navajo Blue, Hopi Blue, Yoeme Blue, and Taos Blue demonstrated that these landraces were genetically related. Phenotypic variability was highest for kernel traits and least for plant traits. Plant, ear, and kernel traits were fairly consistent within and across locations. Principal component analysis and tGBS showed that Corn Belt variety ‘Ohio Blue’ was distinctly different from southwestern landraces. Genotypic analysis displayed that southwestern landraces are genetically closely related, but selection has resulted in differing phenotypes. This study has provided additional insight into the genetic relatedness of southwestern blue maize landraces.

There is increasing interest in the production of landrace blue maize varieties for the production of traditional foods and for specialty (noncommodity) products. Most varieties have soft (floury) endosperm and their suitability for thermo-alkaline processing is not known. We examined the physical and functional properties of eight floury varieties with those of three dent and one flint variety for masa and tortilla production. Results revealed high variability in physical properties of kernels. Significant differences (P0.05) were observed in kernel, flour, masa, and tortilla color. The softer kernels of blue maize varieties had lower (P0.05) cooking times during nixtamalization than those of denser kernels. The results showed variation among varieties (P0.05) in the kernel, masa, tortilla hardness, as well as in extensibility of the tortillas. Nixtamalization affected (P0.05) masa color, resulting in reduced yellow and reddish tones. The gelatinization temperature was the same (P0.05) in all studied landraces for the flour and the masa. The enthalpy was affected (P0.05) by the landrace analyzed for starch gelatinization (P0.05). The landraces studied showed similar (P0.05) starch gelatinization and denaturation temperatures. The storage modulus (G'), loss modulus (G''), and the temperature (TG') of flour and masa-dough were different (P0.05) among different varieties. Southwestern floury varieties can be cooked during nixtamalization for shorter periods than flint and dent varieties to obtain comparable tortilla quality. PRACTICAL APPLICATION: Southwestern blue floury maize varieties are suitable for nixtamalized tortilla production. Variation between varieties was observed for quality parameters. Floury varieties require shorter cooking time but it is recommended that nixtamalization parameters be optimized.

Variation of Kernel Anthocyanin and Carotenoid Pigment Content in USA/Mexico Borderland Land Races of Maize. Maize is the only major cereal crop that displays abundant variation for health-promoting carotenoid and anthocyanin pigments. Traditional farmers in the USA/Mexico Borderland region utilize many land race varieties with diverse kernel characteristics reflecting enculturated preferences, including color. Food prepared using these varieties may provide benefits to human health, but the kernel pigment content, and grain physical and compositional traits, have not been characterized. Seed from 48 diverse accessions representing 18 races of maize originating from the Borderland region were obtained from Native Seeds/SEARCH and planted in replicated nurseries at two locations (Ohio and Arizona) in 2008. We visually determined kernel color and quantified total carotenoid and anthocyanin pigment content of samples obtained from these nurseries using spectrophotometric analysis. Nonpigmented (white) followed by yellow kernel colors were most abundant. Populations with high carotenoid pigment content (i.e., above 40 μg/g) were not observed, whereas many accessions produced ears with mixtures of red, purple, and blue kernels containing anthocyanin pigments. A wide range in anthocyanin pigment content was observed across and within populations—some kernels displayed concentrations above 50 mg/100 g. Kernel hardness was determined visually, and protein and oil content were determined by near-infrared spectrometric analysis. Flinty (hard) followed by floury (soft) kernel types were most abundant. Carotenoid content was highest in orange- and yellow-colored pop-type kernels. Anthocyanin content was highest in blue- and purple-colored floury and flint-type kernels. Kernel weight, protein, oil, and carotenoid content were significantly affected by location. Preservation of culturally-adapted varieties with diverse kernel pigments is important not only because of their genetic diversity—they also may contribute to enhanced human health and nutrition.

Lyimo H.J.F., Pratt R.C., Mnyuku R.S.O.W. (2013): Infection process in resistant and susceptible maize (Zea mays L.) genotypes to Cercospora zeae-maydis (type II). Plant Protect. Sci., 49: 11–18. The infection process of Cercospora zeae-maydi s type II (syn. Cercospora zeina Meisel and Korsman) in resistant, moderately resistant and susceptible maize genotypes was studied in the greenhouse under artificial inoculation. The percent spore germination, germ tube growth and formation of mature appressorium on leaves at 24, 36, 48, and 72 h after inoculation did not differ between resistant, moderately resistant, and susceptible maize genotypes ( P ≤ 0.05). More germlings were established after penetration on susceptible than resistant and moderately resistant maize genotypes at 72, 96, 120, and 144 h after inoculation. The hyphal wefts in cells of resistant and moderately resistant genotypes were shorter than in susceptible genotypes ( P ≤ 0.05). The slow pathogen growth was associated with a reduced number of conidiophores per stroma, spores per unit area and smaller lesions. The reduced pathogen growth after penetration suggests possible involvement of pathogen growth inhibitory substances in maize resistance to C. zeae-maydis type II .

Gray leaf spot is one of the most important yield-limiting diseases of maize (Zea mays L.) and it is more severe in reduced tillage cropping where over-seasoning soilborne inoculum from infected crop debris provides primary inoculum for infection of the newly planted maize. The objective of this study was to investigate the effects of intercropped beans on movement of soil surface inoculum and its overall impact on gray leaf spot severity and yield of maize. Conventional tillage with minimum soil surface inoculum was included for comparison. Trials were conducted in two cropping seasons using resistant (‘UH6303’), moderately resistant (‘Staha’) and susceptible (‘Pannar’) maize varieties. Pooled data for susceptible maize during two growing seasons indicated that the area under disease progress curve (AUDPC) in the inter-cropping treatments was reduced by 12%, 15% and 23% in no-till, minimum, and conventional tillage treatments, respectively, compared to non-intercropping (P ≤ 0.05). The rate of disease increase (r) and the number of spores trapped during the season had similar trends. A moderately resistant cultivar displayed results similar to the susceptible cultivar, whereas treatment effects on resistant genotype were not significant. Yield was 21% higher in the intercropped compared to non-intercropped maize. Spore counts of Cercospora zeae-maydis trapped in the inter-cropping treatment were lower than in non-intercropped maize (P ≤ 0.05). It is concluded that the bean canopy in maize/bean intercrops created a barrier to movement of soilborne spores into the maize canopy, thus minimizing the number of leaves infected by wind-borne, and rain splash. The concomitant use of multiple management options (conventional tillage + inter-cropping + resistant variety) provided superior reduction of gray leaf spot severity and increased yield of maize.

The objective of this study was to assess the aggressiveness and adaptation of Cercospora zeae-maydis the causal of grey leaf spot of maize in low-, mid- and high-altitude maize agro-ecologies. Field and laboratory studies were carried out to assess components of resistance, pathogen aggressiveness, sporulation, culture variations and morphological features of C. zeae-maydis isolates. Pathogen aggressiveness and morphological features differed among 30 isolates of C. zeae-maydis collected at different altitudes (p ≤ 0.05). Conidiophores per stroma between isolates ranged from 3.3 to 9.2 μ, conidiophore length 22.4–93.2 μ and colony growth rate ranged from 1.2 to 3.9 mm−1. High-altitude isolates grew 0.25 mm per day faster (9.3%), formed 1.1 cm longer lesions (25.9%), produced 1.1 × 104 more spores per cm2 of the lesion (13.6%) and formed symptoms 1 day earlier than low-altitude isolates. Prevalence of high numbers of aggressive isolates in low-altitude agro-ecologies indicates increased adaptation of C. z...