Browsing by Author "Ghising, Kiran"

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Impact of Ragl Aphid Resistant Soybeans on Binodoxys communis (Gahan) (Hymenoptera: Braconidae), a Parasitoid of Soybean Aphid Aphis glycines Matsumura (Hemiptera: Aphididae )
(North Dakota State University, 2011) Ghising, Kiran
After its discovery in North America during the summer of 2000, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) became a major pest of the soybean, Glycine max (L.) Merr., in most soybean growing regions of the United States. The use of insect-resistant plant varieties and natural enemies, important components of Integrated Pest Management (IPM), when applied solely have the potential to be effective measures for controlling soybean aphids. However, resistant host plants may influence natural enemies in beneficial or detrimental ways, thereby altering their effectiveness when the two strategies are combined. Therefore, we investigated how a resistant variety impacts fitness of a biological control agent to understand its compatibility for pest management of the soybean aphid. A near isogenic susceptible soybean variety without the Ragl gene and a resistant variety with the Ragl gene were used to determine the effect of the Ragl on the development and fitness of the soybean aphid parasitoid, Binodoxys communis Gahan (Hymenoptera: Braconidae). Before testing for effects of the Ragl gene on the parasitoid, we first validated the expression of the Ragl gene and confirmed that these plants were resistant to soybean aphids by determining the growth rate of soybean aphids on both resistant and susceptible plants. The soybean aphid population and per capita growth rate were significantly higher when reared on susceptible soybean plants compared to resistant plants. In addition, polymerase chain reaction (PCR) was used to verify the genotypes and the presence of the Ragl gene in some of the plants used in the growth rate experiment. Results of the soybean aphid growth rate experiment combined with the results of the PCR helped to validate the expression of the Raglin the resistant plants used in our experiments. To determine the impact of these resistant plants on parasitoids, the total numbers of mummies (parasitized soybean aphids) produced and adult parasitoid emergence were compared for parasitoids that were given aphid hosts from either susceptible or resistant plants. Parasitoid fitness was measured in terms of parasitoid development time, their body length, and their metatibiae length. We found a higher number of mummies in susceptible soybean plants than in the resistant plants as well as a higher emergence rate of adult parasitoids from the mummies reared on susceptible plants. The development time from mummy to adult parasitoid emergence was only one day longer with aphid hosts from resistant plants compared to susceptible plants. Despite some difference in the size of parasitoids from resistant and susceptible plants, very few parasitoids completed development on resistant plants. In summary, our results indicate poorer establishment and reproductive performance of B. communis from soybean aphids on resistant plants compared to soybean aphids on susceptible plants. This suggests that widespread adoption of resistant soybean plants might be detrimental to the overall sustainability of this parasitoid and its ability to help control soybean aphids. We did, however, find that at least some B. communis could successfully develop and emerge on soybean aphids from resistant plants, suggesting that there is at least some possibility that the parasitoid could survive and assist in aphid management even if the Rag 1 resistant plants become commonplace. The parasitoid's relative fitness and reproductive output will likely play important roles in ultimately determining the short- and long-term compatibility of utilizing both B. communis and resistant soybean plants for soybean aphid control.
Screening of the USDA Core Collection of Common Bean for Reaction to Halo Blight and Identification of Genomic Regions Associated with Resistance
(North Dakota State University, 2016) Ghising, Kiran
With only three sources of resistance currently known to race 6 of Pseudomonas syringae pv. phaseolicola (Burkholder) (Psp) which causes halo blight, an important bacterial disease of common bean, there is an urgent need to identify additional sources of resistance. Therefore, 283 accessions of common bean from the USDA-NPGS core collection were evaluated for resistance to race 6 of Psp under greenhouse conditions. Using unifoliate leaf inoculation method, a total of 13% of accessions were resistant. Five of these accessions, PI 201329, PI 309810, PI 310826, PI 319592, and PI 533259, displayed the highest levels of resistance with mean halo blight score of 1.1. Unifoliate vs trifoliate inoculation methods were also evaluated. Significantly higher mean (4.0) and range (1.0-7.0) of halo blight severity was observed at trifoliate stage compared to unifoliate stage, 2.0 and 1.0-2.4, respectively. A significant positive but weak correlation (r2=0.17) of halo blight severity between trifoliate and pod inoculation methods within an individual plant suggests that disease resistance may be controlled by independent genes prevalent at each plant developmental stage. Halo blight severity observed in trifoliate leaves and pods under greenhouse condition was later validated under field condition. Significantly higher mean disease score and range of 4.7 and 2.3-7.1 were reported at pod stage compared to 3.6 and 2.0-6.6, respectively, at trifoliate stage. However, PI 313217 showed consistent resistant reaction across all plant development stages, i.e., unifoliate, trifoliate, and pod, under both field and greenhouse conditions. A significant but weak correlation (r2=0.21) between halo blight severity in trifoliate leaves and pods under field condition confirmed the greenhouse results. To identify genomic regions associated with resistance to race 6 of Psp, genome-wide association mapping study (GWAS) was employed using 197 accessions and 4707 single nucleotide polymorphism (SNP) markers. Three significant regions were identified, of which two novel regions in Pv04 and one in Pv05 controlled for 19% of the phenotypic variation. The significant SNPs could be used in marker assisted selection (MAS) for the improvement of common bean breeding program with focus on resistance to race 6 of Psp.