Phytophthora Sojae Infecting Soybean: Pathotype Diversity, New Sources of Resistance and Interaction with the Soybean Cyst Nematode

<p>Phytophthora root and stem rot, caused by <em>Phytophthora sojae</em> Kaufmann and Gerdemann, is an important disease of soybean (<em>Glycine max</em> L.) in South Dakota. To gain a better understanding of the importance of P. sojae in South Dakota, specifically pathotype diversity, identification of new resistance sources and the interaction with the soybean cyst nematode (<em>Heterodera glycines</em> Ichinohe, SCN), this research was undertaken with the following objectives - 1) to characterize the pathotype diversity of <em>P. sojae</em> causing Phytophthora root and stem rot on soybean in commercial fields in South Dakota; 2) to compare inoculation methods to evaluate for partial resistance to<em> P. sojae</em> on soybean and identify new sources of resistance to two virulence pathotypes of <em>P. sojae</em> in a recombinant inbred line (RILs) population derived from the cross between cultivated <em>Glycine max</em> (cv. Surge) and wild Glycine soja (PI 468916); and 3) to study the interaction between SCN and <em>P. sojae</em> on soybean. In order to achieve the objectives, a total of 114 isolates of<em> P. sojae</em> were recovered from soil samples covering 30 counties in South Dakota during a three year survey (2013 - 2015), of which 70 <em>P. sojae</em> isolates were pathotyped using 13 standard soybean differentials. Results suggest that mean complexity of the P. sojae pathotypes have increased over time and over 85% of the P. sojae isolates were able to defeat<em> Rps</em>1a, <em>Rps</em>1c and <em>Rps</em>1k that are commonly deployed <em>Rps</em> genes in the commercial cultivars of South Dakota. In order to find new sources of partial resistance to<em> P. sojae,</em> a qualitative comparison among three inoculation methods (inoculum layer test, tray test and rice grain inoculation) was accomplished in the greenhouse. Based on the recovery of<em> P. sojae</em> isolates (%), inoculum layer method was adopted to screen 100 recombinant inbred line (RIL) for partial resistance to two virulence pathotypes of<em> P. sojae</em> identified in South Dakota [PS-15-TF3 that is virulent on all 13 soybean differentials and PS-14-F14 that is virulent on only one differential (Rps7)]. As compared to the parents of the RIL population, [<em>Glycine max</em> (cv. Surge) and wild <em>Glycine soja</em> (PI 468916)] we found 9 RILs that had relatively shorter lesion length (0 to 5 mm) when inoculated with either of the <em>P. sojae</em> isolates. To study the interaction between SCN and <em>P. sojae</em> on soybean, a greenhouse experiment was set up in a completely randomized design in a factorial arrangement with four soybean cultivars (Jack, Surge, William 82 and Williams). Two isolates of <em>P. sojae</em> representing two different virulent pathotypes (PS-15-TF3 and PS-14-F14) and SCN HGtype 0 representing the most commonly found HG-type in South Dakota was used to perform inoculations. For all the cultivars, we observed that the lesion length was caused by<em> P. sojae</em> was increased in the presence of SCN relative to <em>P. sojae</em> treatment. However, SCN population was reduced in the presence of both the pathogens. The findings of our study highlight the high pathotype diversity of <em>P. sojae</em> and and increased lesion size when <em>P. sojae</em> co-infects with SCN. This information will help with the development of effective and improved strategies for managing Phytophthora root and stem rot through deployment of resistant genes in commercial soybean varieties that are likely to be more durable, managing SCN to reduce severity of Phytophthora root rot, and incorporation of identified resistance to <em>P. sojae</em> in RIL population for future breeding efforts.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation - Open Access

Discipline thesis:degree_discipline

Agronomy, Horticulture, and Plant Science

Year dc:date.available

2017

Author dc:creator

• Chowdhury, Rawnaq Nazneen

Contributors dc:contributor

• Emmanuel Byamukama
• Febina M. Mathew

• interaction
• partial resistance
• pathotype
• Phytophthora
• soybean
• Agricultural Science
• Agronomy and Crop Sciences
• Plant Sciences

Licence

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/1186

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-2188