Location: Vegetable Research
Project Number: 6080-22000-029-031-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2021
End Date: Sep 30, 2022
Reniform nematode (Rotylenchulus reniformis, RN) is one of the most damaging plant-parasitic nematodes of sweetpotato in the southern U.S. (1,2). Upon infection, RN feeds on roots and greatly reduces the quantity, size, and quality of storage roots. Heavily infested sweetpotato storage roots often develop cracks making them unmarketable (2). In many cases, misdiagnosis occurs mainly because the foliage symptoms resemble nutrient deficiency or water stress, and RN infected roots do not produce visible symptoms (2). Crop rotation is not an effective management strategy for this nematode because of its ability to persist in soil up to 20 years in the absence of suitable hosts, and its ability to quickly rebound to damaging levels when a susceptible host becomes available (2,3). A few fumigant nematicides are available that can suppress RN populations, however, increased cost of nematicides and their adverse effects on health and the environment make chemical control methods unfavorable (3,4). Use of host plant resistance is the most economical approach to managing nematodes in the field; however, there are no sweetpotato cultivars with resistance to reniform nematode currently available. By identifying new sources of host resistance to RN, we will be providing breeders and growers with tools to manage these nematodes in the field.
We propose to evaluate a core set of 96 sweetpotato (Ipomoea batatas) clones from the USDA, ARS, Plant Genetic Resources Conservation Unit (PGRCU; Griffin, GA) genebank (table 1). These PIs were selected based on genomic resequencing data to best represent genetic diversity present in the collection. RN populations maintained on suitable hosts in a greenhouse at Clemson University will be used to screen the selected PIs in greenhouse trials in summer 2022. Greenhouse screening will be performed at Clemson University (Clemson, SC) according to well established protocols used to screen for RN resistance (5). Sweetpotato slips will be rooted in Deepot™ containers filled with a heat sterilized sand:soil medium, and arranged into a randomized complete block design with four replications. Once roots are established (2-3 weeks), each pot will be inoculated with 1,000 RN vermiform life stages (VLS). Inoculated plants will be maintained for an additional 8 weeks post inoculation to allow nematodes to infect and reproduce. Nematode reproduction will be measured in terms of i) number of reniform nematode eggs per root system, and ii) number of VLS per 100 cm3 soil. Nematode eggs will be extracted by agitating infected root systems for 4 minutes in a 10% NaOCl solution, and then rinsing through stacked 8” sieves (#60, #200, #500) to collect eggs (6). The VLS will be extracted using centrifugal-sugar flotation technique (7). Extracted eggs and VLS will be counted by hand using specialized counting dishes under a dissecting microscope. The relative reproductive index will be estimated and is calculated from the number of nematode eggs per gram of root weight and number of VLS per 100 cm3 soil for each plant divided by the value for the susceptible control cultivar Covington. These greenhouse screens will provide information that is currently lacking regarding the relative resistance of each sweetpotato PI to RN. Those lines that show the highest level of resistance will be useful for further evaluation for resistance to RN in grower’s fields.