Interactive effects of cucurbitacin-containing phytonematicides and biomuti on growth of citrus rootstock seedlings and accumulation of nutrient elements in leaf tissues

Abstract

Cucurbitacin-containing phytonematicides and a variety of unidentified soil microbes in suppressive soils (Biomuti) had been consistent in suppression of population densities of root-knot (Meloidogyne spp.) nematodes on various crops. However, information on suppressive effects of cucurbitacin-containing phytonematicides and Biomuti on citrus growth and suppression of the citrus nematode (Tylenchulus semipenetrans) had not been documented. The objective of this study therefore, was to determine the interactive effects of Nemarioc-AL and Nemafric-BL phytonematicides and Biomuti on growth and nutrient elements in leaf tissues of Poncirus trifoliata rootstock seedlings under greenhouse and field conditions. Uniform six-month-old citrus rootstock seedlings [Du Roi Nursery (Portion 21, Junction Farm, Letsitele)] were transplanted in 4 L plastic bags filled with growing mixture comprising steam-pasteurised (300°C for 1 h) loam and compost (cattle manure, chicken manure, sawdust, grass, woodchips and effective microorganisms) at 4:1 (v/v) ratio and placed on greenhouse benches. A 2 × 2 × 2 factorial experiment with the first, second and third factors being Nemarioc-AL phytonematicide (A) and Nemafric-BL phytonematicide (B) and Biomuti (M), were arranged in randomized complete block design, with 10 blocks. The treatment combinations were A0B0M0, A1B0M0, A0B1M0, A0B0M1, A1B1M0, A1B0M1, A0B1M1 and A1B1M1, with 1 and 0 signifying with and without the indicated factor. Treatments were applied at 3% dilution for each product as substitute to irrigation at a 17-day application interval. Under greenhouse conditions, seedlings were irrigated every other day with 300 ml chlorine-free tap water. Under field conditions, the study was executed using similar procedures to those in the greenhouse trial, except that the citrus seedlings were transplanted directly into the soil of a prepared field and seedlings were irrigated using drip irrigation for 2 h every xxi

other day. At 64 days after transplanting, plant growth variables were measured and foliar nutrient elements were quantified using the Inductively Coupled Plasma Optical Emission Spectrometry (ICPE-9000). Data were subjected to analysis of variance using SAS software. Significant second and first order interactions were further expressed using the three-way and two-way tables, respectively. At 64 days after the treatments, under greenhouse conditions Nemarioc-AL × Nemafric-BL × Biomuti interaction was not significant (P ≤ 0.05) on plant variables of seedling rootstocks in both experiments. In contrast, the Nemarioc-AL × Biomuti interaction was highly significant (P ≤ 0.01) on stem diameter, contributing 52% in TTV of the variable in Experiment 1 (Table 3.1), whereas in Experiment 2 the interaction was highly significant on dry shoot mass, contributing 33% in TTV of the variable (Table 3.2). Relative to untreated control, the two-way matrix showed that the Nemarioc-AL × Biomuti interaction, Nemarioc-AL phytonematicide and Biomuti each increased stem diameter by 1%, 12% and 5%, respectively (Table 3.3). Relative to untreated control, the two-way matrix table showed that Nemarioc-AL × Biomuti interaction increased dry shoot mass by 10%, whereas Nemarioc-AL phytonematicide and Biomuti each increased dry shoot mass by 23% and 17%, respectively (Table 3.4). Nemarioc-AL × Nemafric-BL × Biomuti interaction was not significant (P ≤ 0.05) for all plant growth variables in both experiments. However, Nemarioc-AL × Nemafric-BL interaction was significant for leaf number and stem diameter contributing 45% and 29% in TTV of the respective variables in Experiment 2 (Table 4.1). Relative to untreated control, two way matrix table showed that the Nemarioc-AL × Nemafric-BL interaction and Nemafric-BL phytonematicides each increased stem diameter by 8% and 11% respectively, whereas Nemarioc-AL phytonematicides reduced stem diameter by 2% (Table 4.2). Also using two-way matrix table showed that Nemarioc-AL and Nemafric xxii

BL phytonematicides each increased leaf number by 1% and 7% respectively, whereas the Nemarioc-AL × Nemafric-BL interaction increased leaf number by 6% (Table 4.2). Nemafric-BL × Biomuti interaction was significant for stem diameter contributing 29% in TTV of the respective variable in Experiment 2 (Table 4.1). Using two-way matrix table showed that Nemafric-BL × Biomuti interaction and Nemafric-BL phytonematicide each increased stem diameter by 7%, whereas Biomuti alone reduced stem diameter by 6% (Table 4.3). Under greenhouse conditions, the second order Nemarioc-AL × Nemafric-BL × Biomuti interaction was highly significant for foliar Mg, contributing 5% in TTV of the variable in Experiment 1 (Table 3.4). Relative to untreated control, the three-way matrix table showed that the three factors, Nemafric BL phytonematicide and Biomuti each reduced Mg by 33%, 35% and 53%, respectively, whereas Nemarioc-AL phytonematicide increased Mg by 12% (Table 3.5). Nemarioc-AL × Biomuti interaction was highly significant for foliar Mg, contributing 9% in TTV of the variable in Experiment 1 (Table 3.4). Relative to untreated control, the two-way matrix table showed that the Nemarioc-AL × Biomuti interaction and Nemafric-BL phytonematicide reduced Mg by 42% and 12%, respectively, whereas Nemarioc-AL phytonematicide alone increased Mg by 14% (Table 3.6). Nemarioc-AL × Biomuti interaction was highly significant for foliar Ca and Mg, contributing 59 and 4% in TTV of the respective variables in Experiment 1 (Table 3.4). Also using two-way matrix table showed that Nemarioc-AL phytonematicide and Biomuti separately reduced Ca by 12% and 22% respectively, whereas the Nemarioc-AL × Biomuti interaction increased Ca by 1% (Table 3.7). Relative to untreated control, the Nemarioc-AL × Biomuti interaction, Nemarioc-AL phytonematicide and Biomuti reduced foliar Mg by 26%, 21% and 33%, respectively (Table 3.7). Nemafric-BL × Biomuti interaction was highly significant for foliar Mg and P, contributing 50 and 21% xxiii

in Experiment 1, whereas in Experiment 2 the interaction was significant for foliar Ca and Mg, contributing 41% and 38% in TTV of the respective variables (Table 3.4). Relative to untreated control, the two-way matrix table showed that Nemafric-BL phytonematicide and Biomuti individually reduced Mg by 60% and 51%, respectively, whereas the Nemafric-BL × Biomuti interaction reduced Mg by 38% (Table 3.8). Also, in the two-way matrix table the Nemafric-BL × Biomuti interaction and Nemafric-BL phytonematicide each reduced Mg by 13% and 2%, respectively, whereas Biomuti alone increased P by 17% (Table 3.8). Relative to untreated control, Nemafric-BL phytonematicide and Biomuti reduced Ca by 29% and 18%, respectively, whereas Nemafric-BL × Biomuti interaction reduced Ca by 14% (Table 3.9). Using two-way matrix table showed that Nemafric-BL phytonematicide and Biomuti separately reduced Mg by 21%, whereas the Nemafric-BL × Biomuti interaction reduced Mg by 16% (Table 3.9). Interaction of Nemarioc-AL × Nemafric-BL × Biomuti had no significant effect on K, Na and Zn in both experiments. Under field conditions, the second order Nemarioc-AL × Nemafric-BL × Biomuti interaction was not significant for all the nutrient elements in Experiment 1. Nemarioc-AL × Biomuti was significant for Ca, K and highly significant for Mg and P, contributing 31, 8, 23 and 19% in TTV of the respective variables in Experiment 1 (Table 4.4). Relative to untreated control, two-way matrix table showed that Nemarioc-AL phytonematicide and Biomuti each increased Ca by 15% and 26% repectiviely, whereas the Nemarioc-AL × Biomuti increased Ca by 17% (Table 4.5). Interaction of Nemarioc-AL × Biomuti, Nemarioc-AL phytonematicide and Biomuti each reduced Mg by 48%, 70% and 37% (Table 4.5). Also using two-way matrix table showed that Nemarioc-AL phytonematicide and Biomuti each increased P by 4% and 5% respectively, whereas the Nemarioc-AL × Biomuti interaction increased P by 50% (Table 4.5). Realative to untreated control, xxiv

Biomuti and Nemarioc-AL phytonematicide each reduced K by 10% and 5% respectively, whereas the Nemarioc-AL × Nemafric-BL interaction reduced K by 38% (Table 4.7). Nemafric-BL × Biomuti interaction was highly significant for Mg and Zn, contributing 11% and 29% in TTV of the respective variables in Experiment 1 (Table 4.4). Relative to untreated control, two-way matrix table showed that Nemarioc-AL phytonematicide and Biomuti separately increased Mg by 1% and 19% respectiviely, whereas the Nemafric-BL × Biomuti interaction reduced Mg by 43% (Table 4.6). Nemafric-BL × Biomuti interaction, Nemafric-BL phytonematicide and Biomuti each reduced Zn by 35%, 31% and 64% (Table 4.6). Using three-way matrix table showed that the Nemarioc-AL × Nemafric-BL × Biomuti, Nemarioc-AL × Nemafric-BL, Nemarioc-AL × Biomuti and Nemafric-BL × Biomuti interactions each increased Ca by 44%, 18%,10% and 24% (Table 4.8). Further the matrix showed that Nemarioc-AL, Nemafric-BL phytonematicides and Biomuti each increased Ca by 25%, 31% and 23% (Table 4.8). Under both greenhouse and field conditions, although second and first order interactions were not consistent of various variables, results demonstrated that the three products interacted significantly for various products. In conclusion, the study suggested that these innovative products could be used in combination with Biomuti to stimulate plant growth but had antagonistic effects on accumulation of nutrient elements in P. trifoliata rootstock seedlings, suggesting that the products should be applied separately.