Tuber yield, infestation and quality assessment of potato genotypes, partially resistant to Meloidogyne chitwoodi

As part of developing a partial resistance test for potato genotypes resistant to M. chitwoodi; growth, fresh tuber weight, level of tuber infestation and quality loss were studied under greenhouse conditions. Results from four successive experiments were combined. The study involved 7 genotypes with resistance to M. chitwoodi and 1 with resistance to G. pallida. Désirée was used as a control. Plants were inoculated with densities ranging from 0.0625 to 256 J2 (g dry soil)-1 in a 2 log series. Height as growth indicator was measured every week while, fresh tuber weight, tuber infestation and quality were measured at harvest. Also, pots with different volume 10, 5, 3 and 2 kg were used to explore the idea of testing both resistance and yield plus quality loss in smaller and cheaper pots without affecting the nematode-plant system. All data were treated equally in a meta-analysis and relevant models were used to describe the pattern of the data. Plant height showed normal logistic growth in all experiments. Plant height was positively affected by increasing Pi and negatively by pot size. In general growth was delayed. Tuber yield was not affected in four out of 8 genotypes. The four other genotypes and cv. Désirée showed a decrease of fresh tuber weight with minimum yields ranging from 0.40 to 0.84 and 0.75, respectively. In two tested starch potato genotypes an additional decrease of starch content was measured. Tuber infestation levels were reduced and quality was improved compared to the susceptible control and MDG2, with more than 90% of the pots containing clean tubers, with the exception of genotype 2011M1. Quality, expressed as Tuber-Knot Index, was well below < 10, indicating that all genotypes were acceptable for industrial processing.