Influence of priming potato ( solanum tuberosum) seeds in solutions of three phytonematicides on potato growth and nematodes

Abstract

Although potato seed priming in water is not allowed for quality-related reasons in tubers of the produced crop, it was viewed as necessary to use the technique as a carrier of active ingredients of phytonematicides, with the hope that should the technique work, then other solutions could be used for priming of potato tuber seeds. The objectives of this study were to investigate the feasibility of using potato seed tubers as carriers of cucurbitacin A, cucurbitacin B and momordin from triterpenoid- containing phytonematicides to improve management of nematode population densities in potato plants under greenhouse, microplot and field conditions, respectively. In single treatments (A1B0M0, A0B1M0 and A0M0B1), potato seed tubers were without any phytotoxicity in 3% solutions, in any two permutations (A1B1M0, A1B0M1 and A0M1B1) at 1.5% each and at three permutations (A1B1M1) at 1% each, for 7 h and then dried under shade for 2 h prior to planting. Twenty-cm-diameter plastic pots were filled with 2 700 ml growing medium under greenhouse conditions and placed on benches at 0.3 m × 0.2 m spacing. Under microplot 30-cm-diameter plastic pots were used and pots were then inserted into 20-cm-deep holes at 0. 5 m × 0.5 m spacing and under field conditions potato seed tubers were set at 30-cm-depth with a 0.6 m × 0.6 m spacing. A 2 × 2 × 2 factorial experiment was laid out in a randomised complete block design, with the eight treatments replicated 7 times. Nemarioc-AL (A), Nemafric-BL (B) and Mormodica (M) phytonematicides served as first, second and third factors, respectively. At 56 days after applying treatments, the A1B1M1 interactions were not significant on all plant variables under greenhouse and field conditions however under microplot the interaction was significant (P ≤ 0.05) on fresh tuber mass, fresh root mass and dry root mass, contributing 28, 26 and 26% in Total treatment variation (TTV) of the respective variables. In contrast, the A1B1M1 xxviii interactions were highly significant (P ≤ 0.01) on chlorophyll content, contributing 43 and 40% in TTV. Generally, relative to untreated control, the second and first order interactions, along with individual treatments, significantly increased fresh tuber mass by 31% relative to the untreated control, except for Nemarioc-AL × Mormodica and Nemafric-BL × Mormodica interactions which were not different to the untreated. The A0B1M1 interaction was highly significant on plant height, stem diameter, chlorophyll content, dry shoot mass, dry root mass and fresh tuber mass, contributing 45, 36, 37, 35, 60 and 35% in TTV of the respective variables under greenhouse conditions similar to the microplot experiment, the interaction relative to the untreated control, also did not have any effect on plant variables. However, under field conditions the first order interaction, A0B1M1, was highly significant on dry root mass, contributing 60% in TTV on the variable. Relative to untreated control, the interaction reduced dry root mass by 14%, which was not different to the effect of Mormodica phytonematicide at 13%, but was significantly different to that of Nemafric-BL phytonematicide. A1B0M1 interaction had significant effects on fresh tuber mass, contributing 33% in TTV on the variable. Relative to the untreated control, the interaction increased fresh tuber mass (yield) by 32%, which was not different to that of Nemarioc-AL phytonematicide at 40%, but significantly different to that of Mormodica phytonematicide at 16%. Nemafric-BL and Mormodica phytonematicides under greenhouse conditions, each reduced dry shoot mass by 18 and 22%, respectively, whereas their interaction effects on the variable did not differ significantly from the untreated control. Similarly, under microplot conditions Mormodica phytonematicide alone significantly reduced plant height by 12%, although this was not different from the effects of Nemafric-BL phytonematicide. Also, the effects of Nemafric-BL phytonematicide on plant height was not different to that of the untreated control. However, Mormodica phytonematicide increased FSM, xxix DSM and FTM by 31, 33 and 19%, respectively. Mormodica phytonematicide effect on the variables was significantly different to the untreated control. The phytonematicide also reduced FRM and DRM by 17% and the effect on the two variable which significantly differed from the untreated control. The second order interaction were not significant on nematode variable under greenhouse and field conditions, but the interaction was significant only on total nematodes in roots, reproductive potential (RP) and final population (Pf) of Meloidogyne species on roots of potato plants and in the soil under microplot conditions, contributing 11, 13 and 10% in TTV on the variables, respectively. Relative to untreated control Nemarioc-AL × Nemafric-BL × Mormodica phytonematicide interaction reduced total nematode, RP and PF by 18, 64 and 18%, respectively, whereas their effects on the variables differed significantly from untreated control. Generally, Nemafric-BL × Mormodica interaction consistently in all three experiment reduced all nematodes variables. Nemarioc-AL × Nemafric-BL × Mormodica interactions were only significant on Na, contributing 7% in TTV o the variable. Relative to untreated control the interaction reduced Na by 33% and effects on the variable was significantly different to those of untreated control also Nemarioc-AL, Nemafric-BL and Mormodica alone. However, the second order interactions were not significant in greenhouse and field conditions. The A0B1M1 first order interaction although the interactive effects, contributed highly in TTV on Na and Zn in potato tuber tissues, relative to untreated control, the effects were rather negligent at 2 and 4%, respectively. In all different conditions of the study validating that potato seed tubers could be used as carriers of active ingredients of phytonematicides when used through the priming technology. The Nemafric-BL and Mormodica phytonematicide interactions consistently reduced population densities of the Meloidogyne species and increased yield under microplot and field experiments.