Project Details:

Title:
Determination of Heterodera glycines types for improved soybean cyst nematode management in South Dakota

Parent Project: This is the first year of this project.
Checkoff Organization:South Dakota Soybean Research and Promotion Council
Categories:Nematodes, Breeding & genetics
Organization Project Code:
Project Year:2015
Lead Principal Investigator:Emmanuel Byamukama (South Dakota State University)
Co-Principal Investigators:
Gregory Tylka (Iowa State University)
Keywords: Genetic Resistance - Soybean Cyst Nematode, HG Types, Soybean Cyst Nematode, Soybean Cyst Nematode - Assays

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Information and Results

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Project Summary

The soybean cyst nematode causes significant yield loss in soybeans annually in South Dakota, but its effective management depends on knowing the extent of its occurrence and Heterodera glycines (HG) types in South Dakota. HG type testing will be done on soil samples collected from counties and the SCN extracted. Extracted eggs and juveniles will be transferred to soybean differential lines. The reproduction index on the SCN populations will be used to determine the occurrence and frequency of the different HG types. Several commercial soybean cultivars will be screened for SCN resistance in the greenhouse and the field to determine if the resistance genes of these cultivars can limit SCN populations in South Dakota from increasing and still yield well.

This study will highlight the SCN diversity in South Dakota and the implications this diversity has on SCN management. Results from the cultivar screening will inform growers which SCN resistance genes are effective for South Dakota's prevalent SCN HG types. This project will also track SCN movement across counties and provide free SCN soil testing for South Dakota soybean farmers. This is significant since in 2013 they tested 1,098 soil samples for SCN. The goal of this project is to continue activities helping farmers better manage this major pest of soybean.

Project Objectives

1. Continue testing soils for SCN for growers.
2. Determine the distribution of the HG types in South Dakota.
3. Screen for resistance among common soybean cultivars grown in South Dakota.

Project Deliverables

This project will also track SCN movement across counties and provide free SCN soil testing for South Dakota soybean farmers. This is significant since in 2013 they tested 1,098 soil samples for SCN. The goal of this project is to continue activities helping farmers better manage this major pest of soybean.

Progress of Work

Updated October 3, 2015:
Objective 1: Monitoring the occurrence of SCN in SD. During the FY15, 1,313 soil samples were submitted to the Plant Diagnostic Clinic for SCN testing. Of these, 40% were positive for SCN. This is higher SCN prevalence than 2014 samples, indicating continued spread of SCN in the state. Detection of SCN was confirmed for the first time in Campbell County. This implies SCN is continuing to spread further north and west of the state. The results of SCN testing were communicated back to the submitters with recommendations for management for those that were positive. Although these samples were voluntary submissions and therefore not truly random samples, still 40% prevalence indicates the risk of SCN to be increasing in South Dakota.

Objective 2: Determination of HG types that occur in South Dakota. To determine HG types, 250 soil samples were collected from 7-8 arbitrarily selected fields in each of the 28 counties. The soil samples were tested for SCN in the lab. Of these, 33% were positive for SCN with eggs and juveniles count ranging from 50 to 65,200 per 100cm3 of soil. Soil samples that had sufficient SCN egg count had SCN extracted and infested to 7 SCN differential lines in constant temperature water bath (Fig. 1.). The SCN differential lines used were: 1(Peking), 2 (PI88788), 3 (PI90736), 4 (PI 437654), 5 (PI209332), 6 (PI89722), and 7 (Cloud). Soybean cv. Willium 82 was included as a susceptible check and each of the differential lines and susceptible check were replicated four times. For soil samples with insufficient SCN numbers, SCN was first increased on a susceptible cultivar and then infested to the SCN differential lines. After 35 days, the differential lines and the susceptible check were removed from the water bath and SCN female cysts on the roots extracted and counted. A female index (FI) was calculated based on the number of female cysts found on each differential line relative to the susceptible check (William 82) as follows: Average no. of female cysts on a differential line x 100 % Average no. of female cysts on William 82 Female indices equal to or greater than 10% in any line was assigned as that HG type. A total of 73 HG type tests have been completed. Of these, HG type 7 and HG type 0 were the most predominant (47 out of 73 samples tested) HG type detected (Fig. 2). This indicates that a 64% chance that HG type in South Dakota will be HG type 7 or 0. HG type 0 means that the SCN population could not reproduce beyond 10% relative to the susceptible check on any differential lines. HG type 7 means that the SCN population tested could reproduce > 10% on differential line 7 ((Cloud). Twenty five percent of the SCN population had a reproductive index >10% on PI88788, a common source of SCN resistance used in most commercial soybean cultivars. This indicates the need to rotate within soybean cultivars to avoid further adaptation of SCN populations to this source of resistance. The SCN population that had FI > 10% on PI88788 had also FI>10% on PI 5 and 7. Only five (7%) of SCN populations tested had Female Index >10% on differential line 1 (Peking). Peking is the second most common source of SCN resistance genes used in commercial soybean lines.

Objective 3: Screen major soybean cultivars for resistance against HG types prevalent in SD Host resistance, when available, is the most effective, economical, and sustainable plant disease management practice. Although SCN resistance has been developed, most of the available resistant soybean cultivars have been mainly from one source, PI88788. No information is available how these commercial soybean cultivars with resistance to SCN are adapted to South Dakota SCN populations. We have acquired 34 commercial soybean cultivars from seed companies. These will be screened against the common HG types, namely HG type 0, 2.5.7, and 7 in the second year of this grant.

Final Project Results

In the FY2015--1,313 producer soil samples were analyzed for SCN and results and recommendations provided to the submitters. This number is slightly higher than last year submissions, indicating continued awareness of SCN in the state.

We have determined the Heterodera glycines types for 73 SCN populations collected from SD. Results indicate 25% of the SCN populations tested can reproduce on PI 88788, a common source of resistance used in SD. Of the HG types tested, 29% were HG type 0 (these populations had <10% female index on all SCN differential lines). The majority of SCN populations tested could only reproduce on a single PI line. These results indicate that use of resistance genes available in commercial cultivars is still viable, but should be combined with other management practices to avoid adapted SCN populations increasing.

Benefit to Soybean Farmers


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