Screening fusarium resistant rootstocks for plant parasitic nematode resistance

Authors: SMITH, CODY - University Of Florida; FREEMAN, JOSH - University Of Florida; Burelle, Nancy; Wechter, William - Pat

Submitted to: Proceedings of Methyl Bromide Alternatives Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/10/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: The phase out of methyl bromide has directed research toward alternative methods of managing soil-borne pathogens. A limiting factor in many watermelon producing regions is Fusarium wilt caused by a soil-borne fungus. One method of managing this disease involves grafting a susceptible, high yielding scion onto a resistant rootstock. Preliminary findings have demonstrated that many wilt resistant rootstocks are highly susceptible to root-knot nematodes and other plant parasitic nematodes. Resistance has been demonstrated independently but rootstocks containing resistance to both are not yet commercially available. A concerning issue with rootstocks resistant to Fusarium wilt is that many have not been tested for their susceptibility to plant pathogenic nematodes, more specifically the southern root-knot nematode and the reniform nematode. Plant parasitic nematodes can reduce yield and pose the risk of causing a synergistic disease complex with the fungal pathogen which can predispose the resistant host to fungal susceptibility. For grafting to be a commercially viable Fusarium wilt management tool, resistance to plant parasitic nematodes should also be included in the rootstock cultivar. Experiments were conducted in the spring and fall of 2016 at the North Florida Research and Education Center in Quincy, Florida. Four rootstocks were evaluated in both experiments. In both seasons the cucurbit rootstock ‘Carnivor’ was included as a control because of its known susceptibility to root-knot nematodes. In both experiments the four selected rootstocks were more resistant than the control ‘Carnivor’ in regards to root galling. ‘Bulldog’, and USVL 246, and USVL 252 had lower root knot nematode counts in their root tissue both seasons when compared to the control. ‘SP-6’ and ‘USVL-252’ maintained separation from the control with reniform nematode soil data. Populations of reniform nematode were found in higher numbers in the soil as compared to root tissue due largely to their semi-endoparasitic life cycle. Both plant parasitic nematodes had higher soil numbers in the fall experiment compared to the spring. Little to no root knot disease was observed on the rootstock cultivars tested in these experiments indicating resistance to plant parasitic nematodes.

Technical Abstract: The phase out of methyl bromide has directed research toward alternative methods of managing soil-borne pathogens. A limiting factor in many watermelon producing regions is Fusarium wilt caused by the soil-borne fungi Fusarium oxysporum f.sp. niveum (FON). There is no varietal resistance to FON deployed in triploid seedless watermelon. One method of managing this disease involves grafting a susceptible, high yielding scion onto a resistant rootstock. Preliminary findings have demonstrated that many C. maxima x C. moschata Fusarium wilt resistant rootstocks are highly susceptible to root-knot nematodes and other plant parasitic nematodes. Resistance to FON and Meloidogyne spp. (RKN’s) has been demonstrated independently but rootstocks containing resistance to both are not yet commercially available. A concerning issue with rootstocks resistant to Fusarium wilt is that many have not been tested for their susceptibility to plant pathogenic nematodes, more specifically the southern root-knot nematode (Meloidogyne incognita) and the reniform nematode (Rotylenchulus reniformis). Plant parasitic nematodes can reduce yield and pose the risk of causing a synergistic disease complex with FON which can predispose the resistant host to FON susceptibility. For grafting to be a commercially viable Fusarium wilt management tool, resistance to plant parasitic nematodes should also be included in the rootstock cultivar. Experiments were conducted in the spring and fall of 2016 at the North Florida Research and Education Center in Quincy, FL. Experimental plots were arranged in a randomized complete block design with four replications. Black polyethylene mulch was used in spring and white-on-black mulch in the fall of 2016. Soil was cultivated to a depth of 25 cm prior to bed formation. Rows were spaced 2.44 meters apart, beds were 76.2 cm wide, 20.3 cm tall, and 18.3 m long. Four rootstocks were evaluated in both experiments: ‘Bulldog’ (USDA-ARS), ‘USVL-246’ (USDA-ARS), ‘USVL-252’ (USDA-ARS) and ‘SP-6’ (Syngenta seeds). In both seasons the cucurbit rootstock ‘Carnivor’ (Syngenta seeds) (C. maxima x C. moschata) was included as a control because of its known susceptibility to RKN. In both experiments the four selected rootstocks maintained statistical separation from the control ‘Carnivor’ in regards to RGI. ‘Bulldog’, and USVL 246, and USVL 252 had lower RKN counts in their root tissue both seasons when compared to the control. ‘SP-6’ and ‘USVL-252’ maintained separation from the control with R. reniformis soil data. Populations of R. reniformis were found in higher numbers in the soil as compared to root tissue due largely to their semi-endoparasitic life cycle. Both PPN’s had higher soil numbers in the fall experiment compared to the spring. Little to no root knot symptomology was observed on the rootstock cultivars tested in these experiments implying resistance to PPN’s.