Document Type

Thesis - Open Access

Award Date

2019

Degree Name

Master of Science (MS)

Department

Agronomy, Horticulture, and Plant Science

First Advisor

Shaukat Ali

Abstract

Oat is an important cereal crop, and it is considered to be among the highest used in cereal crops. It is considered among the healthiest grains due to the rich source of the soluble fiber, β-glucan that helps in lowering the cholesterol. Oat production and demand have increased considerably in the past few years due to its health benefits. South Dakota is ranked in the top three largest oat-producing states in the USA. Oat is relatively less susceptible to pest and diseases except for leaf diseases such as crown rust, Drechslera avenae leaf spot, and Stagonospora avenae leaf blotch. Leaf spot diseases like Drechslera avenae leaf spot and Stagonospora avenae leaf blotch can cause high yield losses in oats under conducive environment for disease development. However, no information is available on the prevalence of leaf spot diseases in oats and reaction of oat cultivars to Drechslera avenae leaf spot in South Dakota. Triticale is another cereal crop that plays an important role by serving as a bridge between the rye and wheat in transferring good agronomic traits like yield, winter hardiness, and pest and disease resistance genes to improve wheat quality. Additionally, it is used as a forage and a rotational crop in improving soil health. It is generally considered less prone to pest and diseases; however, it has been reported to be susceptible to some foliar diseases including tan spot, an important disease of wheat. Also, it can serve as an additional inoculum source of tan spot causing pathogen, Pyrenophora tritici-repentis, inoculum/virulence variation when cultivated in the vicinity of wheat. Information on the reaction of triticale to commonly prevalent P. tritici-repentis races1 and 5 is unknown. The objectives of this study were to, 1) conduct a disease survey of leaf spot pathogens associated with oat in South Dakota, 2) characterize a global collection of oat genotypes including commercial cultivars grown in South Dakota, against D. avenae leaf spot in greenhouse; and 3) evaluate a worldwide collection of triticale genotypes for their reaction to tan spot using the pathogen, Pyrenophora tritci-repentis which causes tan spot, race1, race 5, and host selective toxin Ptr ToxA. To achieve these objectives, the diseased leaves samples displaying leaf spots were collected from different oat fields in 2017 and 2018 in South Dakota. The leaf samples were examined for leaf spot pathogens using standard protocols. One hundred fifty-five oat genotypes representative of 33 countries and 366 triticale genotypes from 21 countries were evaluated for their reaction to D. avenae leaf spot and tan spot, respectively at seedlings stage in the greenhouse. Four leaf spot pathogens D. avenae and Stagonospora avenae, Bipolaris victoriae, and Colletotrichum graminicola were observed on the collected oat leaves samples; however, D. avenae and Stagonospora avenae had hhigher prevalence as compared to B. victoriae, and C. graminicola. The 155 evaluated oat genotypes varied in their reaction to D. avenae leaf spot in ranging from susceptible (41.3%), moderately susceptible (28.4%), moderately resistant (15.5%), and resistant (14.8%). All commercial cultivars exhibited a susceptible reaction to D. avenae leaf spot. The results of the 366 triticale genotypes screened for their reaction against P. tritici-repentis race 1 and race 5 exhibited variability in their responses to both races 1 and 5. The majority of genotypes (53%) that evaluated were found either resistant or moderately resistant to race 1. The sensitive reaction against Ptr ToxA observed in only 68 (18.55%) genotypes. In this study, the correlation between susceptibility and Ptr ToxA sensitivity or resistance and Ptr ToxA insensitivity of the genotypes was not observed. Most of the genotypes (64.75%) screened against race 5 developed resistant to– moderately resistant reactions. Our results showed that most of the triticale genotypes harbor resistance against tan spot, races 1 and 5 both at the continent or country level. Ptr ToxA seems not playing a significant role in disease development as reported in previous studies in wheat and rye. The outcomes of this study warrants observing leaf spot pathogens in the state at regular bases and incorporate of resistance to Drechslera avenae leaf spot in oat cultivars grown in future to circumvent any chance of occurring the disease epidemic in the region. Further, oat genotypes exhibited resistance to the disease can be used as sources of resistance in the oat breeding program. Oat genotypes with D. avenae leaf spot resistance should further be tested against S. avenae leaf blotch, another leaf spot pathogen prevalent in the state. Also, triticale genotypes with tan spot resistance should be used when planted nearby wheat area, and in transferring good agronomic traits in wheat to avoid transferring accidental susceptibility to tan spot.

Library of Congress Subject Headings

Oats -- Diseases and pests.
Oats -- Disease and pest resistance.
Triticale -- Diseases and pests.
Triticale -- Disease and pest resistance.
Leaf spots.
Leaf spots -- South Dakota.

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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