Kristen Otto

Inheritance of White Mold Resistance in Phaseolus vulgaris × P. coccineus Crosses

The fungus Sclerotinia sclerotiorum, cause of white mold, is known to attack >400 plant species. It is a widespread problem in dry bean (Phaseolus vulgaris) in the United States, causing >30% average yield losses. Low to moderate levels of resistance are found in dry bean. However, some accessions of P. coccineus (commonly known as scarlet runner bean) possess a relatively higher level of resistance. Our objective was to verify the reaction of 13 known white mold-resistant P. coccineus germ plasms and determine inheritance of resistance in accessions PI 433246 and PI 439534. Pinto Othello was crossed with PI 433246, and the resulting interspecific F1 was back-crossed onto Othello and allowed to produce F2 seed. Similarly, pinto UI 320 was crossed with PI 439534. The F1 was backcrossed onto UI 320 and allowed to produce F2 seed. The two parents, F1, F2, and backcross to dry bean of each set were evaluated in the greenhouse using the straw test at Fort Collins, CO in 2004. All 13 P. coccineus accessions and the two F2 also were evaluated using the modified petiole test at Kimberly, ID in 2005. All 13 P. coccineus accessions were variable in a 2002 straw test when rated for white mold reaction on a 1-to-9 scale, because the mean disease score ranged from 1.9 for PI 433246 to 4.4 for PI 189023 and 8.8 for the susceptible check Bill Z. For the petiole test, when rated on a 1-to-9 scale, the accessions exhibited an intermediate white mold score of 4 or 5 in 2005. In 2004, the susceptible check Othello exhibited a mean score of 7.9 compared with 3.4, 3.2, and 2.1 for PI 433246, UI 320, and PI 439534, respectively. The white mold reaction of PI 433246 and PI 439534 was dominant in their respective F1. The F2 segregation further indicated that white mold resistance in PI 433246 and PI 439534 was controlled by a single dominant gene. These two and other white mold-resistant P. coccineus accessions and selected breeding lines from the interspecific crosses should be useful for future improvement of white mold resistance of pinto and other market classes of dry and green or snap bean.

Relation of Temperature and Rainfall to Development of Xanthomonas and Pantoea Leaf Blights of Onion in Colorado

During the 1996 to 1999 growing seasons, some areas of Colorados onion-growing regions experienced a complex of bacterial diseases including leaf blights caused by Xanthomonas campestris and Pantoea ananatis. Crop losses varied depending on adverse weather (associated with rain, storm, and temperature patterns) and stage of onion plant development. Environmental conditions during vegetative development had no significant association with the initial appearance or subsequent intensity of disease. Both pathogens were active at average high temperatures that ranged from 28 to 35°C during bulbing. Multiple regression models were developed to predict the initial appearance (growing degree day [GDD]) and subsequent Xanthomonas leaf blight intensity (final proportion of disease [FPD]) using macroclimatic meteorological conditions, including July average daily high temperature (Tjmax), August cumulative rainfall (Pa), and cumulative rainfall in July and August (Pja). Initial disease appearance and disease intensity were described by GDD10 = -6,153.43 + 215.50Tjmax - 0.92Pa and FPD = 222.79 - 6.92Tjmax + 0.52Pja, respectively. Pantoea leaf blight initial appearance was strongly associated with July average daily temperatures (Tj) and was described by GDD10 = -5,930.43 + 289.07Tj. Results are discussed in relation to an integrated pest management strategy in Colorado.

Sexual Stage Development of Uromyces appendiculatus and Its Potential Use for Disease Resistance Screening of Phaseolus vulgaris

In June 1989, pycnia and aecia of the bean rust pathogen were observed in eastern Colorado on volunteer plants of pinto bean cvs. UI 114 and UI 126 that grew from seed that remained in the field after harvest the previous season. Harvested aeciospores were viable and produced typical reddish-brown uredinia on unifoliolate leaves of UI 114 seedlings in the greenhouse. Evidence of bean rust overwintering has been confirmed in 10 years from 1989 to 2002 in eastern Colorado and the surrounding region. Overwintering conditions were reproduced at Fort Collins, CO in fall 1992 and spring 1993. Debris treatments had significantly higher disease incidence on stems, total number of lesions on stems, disease incidence on leaves, and total number of lesions on leaves of plants of pinto cvs. UI 114 and Olathe than plants without debris. Bean leaves of both cultivars had significantly higher disease incidence than stems. There also was an increased incidence of aecial infection for UI 114 seedlings that germinated through leaf debris with rust compared with stem debris under greenhouse conditions with abundant moisture. Bean leaf debris smaller than 0.36 mm in diameter resulted in significantly more aecial lesions on UI 114 than larger leaf debris and stem debris. Additional greenhouse experiments demonstrated that diverse collections of naturally occurring, overwintered, rust-infested bean debris from eastern Colorado produced different levels of pycnial and aecial infection on pinto cvs. UI 114, Olathe, and Chase. Chase, currently resistant to the uredinial stage of the prevalent bean rust races in Colorado and surrounding states, had a low incidence of aecial lesions on seedling stems when exposed to pycnial and aecial stages in the greenhouse. These observations indicate that selection of bean rust resistance genes should rely on multiple sources of resistant germ plasm to counter the potential increase in new races that could derive from sexual recombination in bean-production regions.

Pyramiding white mould resistance between and within common bean gene pools

Singh, S. P., Schwartz, H. F., Terán, H., Viteri, D. and Otto, K. 2014. Pyramiding white mould resistance between and within common bean gene pools. Can. J. Plant Sci. 94: 947-954. White mould caused by Sclerotinia sclerotiorum (Lib.) de Bary is a severe disease of common bean (Phaseolus vulgaris L.) in North America and similar production regions. Low to high levels of white mould resistance exist in cultivated and wild common bean and the secondary gene pool. But, cultivars with high levels of resistance are not yet available. The objectives of this study were: (1) to combine or pyramid high levels of resistance from multiple-parent populations between and within gene pools, and (2) to compare the response of pyramided breeding lines (PBL) to four isolates of the white mould pathogen with that of known sources of resistance. Two Andean PBL each derived from an Andean intra-gene pool and inter-gene pool, four Middle American pinto bean PBL from one inter-gene pool multiple-parent population, their seven resistant parents, and susceptible pinto, Othello, were inoculated in the greenhouse with pathogen isolates ARS12D and ND710 at University of Idaho, Kimberly in 2012, and isolates CO467 and NY133 at Colorado State University, Fort Collins in 2013. The percentage of resistant plants for the PBL ranged from 62.5 to 81.9, and mean white mould score from 4.0 to 4.6. The respective values for the white mould resistant parents ranged from 3.1 to 57.0 for the percentage of resistant plants and from 4.8 to 7.5 for the mean white mould score. Furthermore, PBL SE154-1 inoculated with isolate ARS12D, and SE152-6 with isolates ARS12D and ND710 had 100% resistant plants. But, only SE153-1 and SE155-9 inoculated with isolates CO467 and NY133 had significantly (P ≤0.05) higher levels of resistance than the most resistant parents A 195 and VA 19. The pinto bean PBL SE153-1, SE153-6, and SE153-7, and Andean types SE152-6 and SE155-9 were the most resistant among all genotypes inoculated with the four isolates of the white mould pathogen in both greenhouses.

Straw Mulch and Reduced-Risk Pesticide Impacts on Thrips and Iris Yellow Spot Virus on Western-Grown Onions

Abstract. Iris yellow spot virus and its vector the onion thrips, Thrips tabaci Lindeman, are yield-limiting pests of onion, Allium cepa L., throughout the western U.S. In experiments in Colorado during 2005 to 2007, straw mulch applied to the center of onion beds at the early to mid-bulb growth stage reduced abundance of thrips as much as 33% when compared to nontreated plots of transplanted onions. Cumulative thrips-days indicated that straw mulch significantly reduced season-long abundance by 10 to 20% compared with check plots in bare soil. The addition of conventional insecticides (methomyl alternated with lambda-cyhalothrin) was associated with 12 to 27% greater cumulative thrips-days compared to the nontreated check in two experiments. In contrast, a reduced-risk insecticide program (spinosad alternated with azadirachtin) had fewer cumulative thrips-days on both bare soil (15%) and straw mulch (36%) compared to nontreated checks. Enhanced thrips control generally persisted during mid-season and may have contributed to reduced stress from damage by thrips feeding and reduced incidence and/or severity by Iris yellow spot virus during the early to mid-bulb stages of plant growth. Total yield and yield of jumbo-sized onions were increased as much as 13 and 18% by straw mulch compared to bare soil treatments among the individual experiments. Peak abundance of thrips on commercial red onion plants evaluated during 2004 was positively correlated with the incidence of iris yellow spot 40 days (R2 = 0.5864, P = 0.0060) and 54 days (R2 = 0.6086, P = 0.0046) later, indicating that suppressing thrips might provide some control of the disease. Effective long-term management of thrips and iris yellow spot in onion crop systems will depend on a multi-faceted approach that integrates host resistance, modified cultural practices such as straw mulching and irrigation scheduling, and judicious use of reduced-risk insecticides.

Evaluation of Onion Germplasm for Resistance to Iris Yellow Spot (Iris yellow spot virus) and Onion Thrips, Thrips tabaci

Abstract. Onion (Allium cepa L.) is the most economically important monocot besides grasses. The crop suffers severe damage from onion thrips, Thrips tabaci Lindeman, a cosmopolitan and polyphagous insect pest. In addition to causing direct feeding damage, onion thrips is the principal vector of the economically important Iris yellow spot virus (Tospovirus sp., family Bunyaviridae). Any attempt to manage this pathosystem will require a multifaceted approach based on integrated pest management. Host plant resistance is an important foundation to the success of such approaches. A multi-state, multi-disciplinary research project was established to identify, validate, and deliver resistance to this pathosystem for use by the onion industry. As part of the project, diverse onion plant introduction (PI) accessions from the USDA germplasm collection, advanced breeding lines, and commercial cultivars were evaluated from 2009 through 2011 in fields in Colorado. Sixteen, 15, and 10 better performing onion genotypes were selected in 2009, 2010, and 2011, respectively. Of these, PI 264320 (Grano), PI 546140 (San Joaquin), and PI 546192 (Yellow Sweet Spanish) were selected in both 2009 and 2010, and PI 258956 (Calderana 1028) and PI 546188 (Yellow Sweet Spanish Winegar) were selected in all 3 years. These genotypes should be useful to improve commercial cultivars to reduce losses by the two pests.

Thrips tabaci (Thysanoptera: Thripidae) and Iris yellow spot virus Associated with Onion Transplants, Onion Volunteers, and Weeds in Colorado

Abstract. Infestation by onion thrips, Thrips tabaci Lindeman, was determined on transplants of onion (Allium cepa L.) received in Colorado during March and April from out-of-state sources (Imperial Valley, CA; near Phoenix, AZ; and southern Texas) during 2004 to 2008. In the 5 years of the study, 50 to 100% of the transplant lots sampled arrived infested with thrips. Among infested transplant lots, the overall number of thrips averaged 0.15 to 0.63 per plant, with as many as four per plant in some lots. T. tabaci was the dominant thrips species in all seasons and locations of transplant origin. In addition, 19 of 83 (23%) tested lots had plants positive for Iris yellow spot virus. Iris yellow spot virus and T. tabaci were detected in volunteer onion plants as early as 1 May, a few weeks after the summer onion crop was planted, suggesting a possible role of infected volunteer plants in perennation of the virus between onion crops. Iris yellow spot virus and T. tabaci were detected in many common weeds including blue mustard (Chorispora tenella (Pall.) DC), common purslane (Portulaca oleracea L.), field bindweed (Convolvulus arvensis L.), flixweed (Descurainia sophia Webb & Berth.), prickly lettuce (Lactuca serriola L.), and redroot pigweed (Amaranthus retroflexus L.) in early spring near onion fields in Colorado during 2006 to 2009. Confirmation that Iris yellow spot virus and Iris yellow spot virus-infective thrips overwintered in volunteer onions and some common winter annual and perennial weeds emphasizes that managing volunteer onions and weeds is important for management of iris yellow spot, in addition to planting transplants free of thrips and the pathogen.