Screening Improved Wheat-Lines for Plant-Parasitic Nematode Resistance.

Improved wheat lines were field screened for plant-parasitic nematode resistance and tolerance. There were three planting sites and 10 random composite soil samples were collected from each field preplant and at harvest. The plant-parasitic nematodes recovered were of two colonizer-persister(cp) classes-cp2/Pl₂ and cp3/Pl₃.  At harvest  the Pl₂ nematodes  recorded were Tylenchus(42.42%), Psilenchus(54.95%), and Paratylenchus(2.72%) and the Pl₃ were  Pratylenchus (50.17%) , Heterodera (23.24%), Hoplolaimus (11.79%), Meloidogyne(10.41%), and Tylenchorhynchus( 4.39%). The initial and final Pl₂ nematode populations were as follows:  Almota- 365.9 v 167.9, Colton-41.3 v 105.2, and Mokanema-49.9 v 112.8, Pl₂ nematodes per 100 mL soil sample. In Almota Pl₂ nematode populations decreased by 117.93 %( P=0.01), in Colton Pl₂ nematode populations increased by 154.72 %( P=0.01), and in Mokanema the final population increased by 126.05 %( n.s). For Pl₃ nematodes, the final Almota population was reduced to 77.45% of the initial population (292.2 v 226.3) and in Colton the final population increased by 19.49%. On the other hand, the final Pl₃ nematode populations in Mokanema increased by 351.93 %( P= 0.001; 90.7 v 409.9). The mean number of Pl₂ nematodes recorded at harvest, were; 105.2 < 112.8 < 167.9, respectively for Colton-winter wheat, Mokanema-spring wheat, and Almota-winter wheat. For the Pl₃ nematodes it was 226.3 < 276.5 < 409.9, respectively for Almota, Colton, and Mokanema. Pl₃ nematodes are bigger than Pl₂ nematodes and therefore more destructive.  Means therefore of 226.3 to 409.9 Pl₃ nematodes per 100 mL soil sample are 2 to 4x the number of nematodes considered economic thresh hold, requiring management. A study that will include soil analysis is required to account for location differences.