Background/Question/Methods Plant yield is a measure of plant health and healthy plants are efficient photosynthesizers. Efficiently photosynthesizing plants extract their CO₂ from the environment. A reduction of atmospheric CO₂ has a cooling effect. Any agent that is capable of disrupting the photosynthetic processes of crop plants could therefore have a dual effect in the environment.
Plant-parasitic nematodes are the number one biotic cause of crop loss world-wide. Solanum tuberosum and Lycopersicon esculentum are Solanaceae and are staples in Central Arkansas. Their parasitic nematodes were investigated for the first time in an effort to elucidate if they attain economic threshold levels.
Soil samples were collected up to a depth of 20 cm from organically grown potato and tomato farms. Four samples were collected from each farm from alternate ridges, using a foot-driven soil sampler of diameter 6.5 cm. Each soil sample was a composite of six cores. Samples were collected once every four weeks for four months (December-March). In the laboratory, each sample was mixed, 100 mL withdrawn, and nematodes extracted using a combination of decanting, sieving, and the Baermann funnels. The first 15 mL of incubated sample was tapped after 72 hrs and the nematodes quantified and categorized. A paired-t-test was used to compare nematodes of both crop species.
Results/Conclusions Three colonizer-persister (cp) classes of nematodes were recovered from each crop species. These were the Pl₂, Pl₃, and Pl₅, respectively. The Pl₂ genera were Tylenchus costatus, Psilenchus sp., Paratylenchus sp., and Gracilacus sp. The Pl₃ were Helicotylenchus mucronatus, Meloidogyne incognita, Pratylenchus sp., and Rotylenchus buxophilus. The Pl₅ were Xiphinema sp. and an unidentified Longidorid. Except for January, greater numbers of parasitic nematodes were recovered from tomato soils than from potato soils. These differences were statistically significant in most cases, ranging from P>0.05 to P>0.001. Up to 843.3 nemas/100 mL soil was recorded for L. esculentum versus the 462.8 nemas/100 ml soil for S. tuberosum. Clearly L. esculentum were more susceptible to nematode infection than S. tuberosum. Previously, up to 50 nemas/100 ml was reported as economic threshold. Potato recorded over 9x and tomato almost 17x this value. Some symptoms of nematode parasitism included yellowing of leaves, root decortications and galling, stuntedness, tuber blemishes and even plant death. These symptoms coupled with high infestation rates suggest that nematodes significantly reduced crop yield and plant photosynthetic processes.