Mycorrhizal Inoculation of Tomato and Onion Transplants Improves Earliness

Field experiments were conducted near Weslaco, Texas (Lat. 26° 8' N) between 1999 and 2001 to evaluate the field performance of preand post-mycorrhizal inoculations of tomato and onion (2001 only) transplants. In 1999 ‘Heatmaster’ tomato (Lycopersicon esculentum Mill.) transplants were inoculated with Glomes intraradices (Reforestation Technologies, Salinas, CA) at transplanting; in 2000 ‘Heatmaster’ and ‘Florida 47’ plants were treated at transplanting and exposed to two irrigation regimes; and in 2001 ‘Heatmaster’ plants were either preor posttransplant inoculated and grown in a light (Hebbronville) or heavy (Raymondville) textured soil. In all years, cumulative fruit yield by the second and/or third harvest were significantly greater with mycorrhizal-treated plants, but final season yield, fruit number and average fruit weight were usually similar to untreated controls. Marketable yield and fruit number tended to improve when plants were treated with mycorrhizae. Onion (Allium cepa L.) cultivars Granex 1015Y and Terlingua inoculated with mycorrhizae in a seedling mix or at transplanting and planted in Hebbronville and Raymondville soils improved bulb yields and accelerated maturation, but bulb soluble solids at harvest were similar when compared to uninoculated plants. Bulbs from mycorrhizal-treated plants were more uniform in diameter. Bulbs stored at 13.2°C for 120 days suffered less soluble solids and weight loss if they were from mycorrhizal-treated plants. Bulb sprouting was not affected by any treatment. INTRODUCTION Arbuscular mycorrhizal fungi have been shown to provide a level of protection against tomato and onion pathogens (Caron et al., 1986; Torres-Barragan et al., 1996), nematodes (Al-Raddad, 1995), salinity (Copeman et al., 1996; Al-Karaki and Hammad, 2001) and to influence flower biology (Poulton et al., 2002) and plant competition from bahiagrass (Sylvia et al., 2001). Even when given phosphate-containing fertilizers (Waterer and Coltman, 1988; Sharma and Adholeya, 2000), tomato and onion plants can still benefit from the association with mycorrhizal fungi. In field studies involving tomato production and plant/soil water status, it was observed that tomato plants inoculated with Glomus intraradices tended to have higher early-season yields by the second or third harvest. What follows is a summary of several of these studies with respect to seasonal yield distribution in tomato. The response of late fall-planted onion which had been sown or transplanted with or without mycorrhizal inoculation is also reported. MATERIAL AND METHODS G. intraradices from Agroforestry Systems, Salinas, CA was used in these studies. Transplants were grown in 200A Speedling flats. Approximately 1.14 g or 120 propagules/transplant was applied which is equivalent to about 16 kg/ha of product based on a tomato field setting of 14 350 plants/ha. For seedling production, mycorrhizae was thoroughly mixed with bulk media (Sunshine Mix #3), which contained the equivalent 3 g/L or 18 g/flat of G. intraradices inoculum. After field setting, recommended fertilizer, herbicide, and insecticide rates were used (Dainello, 1996). No fungicides were applied. All experiments were randomized complete block designs with 4 replications. At each Proc. XXVI IHC – Transplant Production and Stand Establishment Eds. S. Nicola, J. Nowak and C.S. Vavrina Acta Hort. 631, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 276 tomato harvest, marketable fruit number and weight, cull fruit number and weight, and the number of ripe, unpicked fruit in the field (rotten or damaged by predators) were recorded. Tomato within-row spacings were 0.46 m and row spacings were 1.5 m. Tomato, 1999 Two independent experiments using ‘Heatmaster’ transplants were conducted. In the first trial, treatments consisted of control, kaolin sprays (K), G. intraradices at transplanting (M), and K + M. Plots of 3.6 m were harvested eight times from Julian dates (JD) 123 to 173. In the second trial, transplants with and without G. intraradices, were planted into 3.6 m conventional and no-tilled rye, Secale cereale, prepared plots and harvested eight times from JD123 to JD173. Tomato, 2000 Soil moisture (main plots) were established in a Hebbronville soil and plants of cultivars Florida 47 and Heatmaster were either inoculated with G. intraradices at transplanting or left noninoculated (subplots). Subplots were 3.6 m and 5 harvests were made between JD123 and JD153. High and low soil moisture plots were irrigated at -20 and -40 kPa soil tension, respectively. Tomato, 2001 ‘Heatmaster’ plants were either inoculated with G. intraradices or not at sowing or transplanting and transplanted into Hebbronville and Raymondville soils. Plot length was 4.6 m and 8 harvests were made between JD117 and JD164. Onion, 2000-2001 Fall seeded ‘Granex 1015Y’ and ‘Terlingua’ were either inoculated with G. intraradices or not at sowing or transplanting into Hebbronville and Raymondville soils. Plants were set within a staggered single row at a 15 cm spacing between transplants. Ten uniform bulbs were harvested within each 2.5 m plot to determine yield, bulb diameter and % soluble solids. Bulbs from the Raymondville soil were stored at 13.2°C for 120 days and % water loss, sprouting, and soluble solids (by a hand refractometry) were determined. The Hebbronville site was planted about 3 weeks after the Raymondville site. Both plantings were 4 to 6 weeks later than ‘normal’. RESULTS Marketable tomato fruit yield by harvest date and cumulatively over the season (inserts) are reported in Figures 1-4. Other field attributes, such as fruit cull number and weight, total fruit number and weight, and % marketable fruit, were generally similar and thus not shown. Soil moisture levels in 2000 were statistically similar therefore the data in Figure 3 represent pooled values over moisture levels. With the exception of 2000, cumulative tomato yields were not affected by G. intraradices application (P<0.05) (Fig. 3). Total season yields, pooled over treatments common to all three years, were also not affected by G. intraradices application (data not shown). However, in most tomato experiments, mycorrhizal application increased yield at the second and third harvests (Figs. 1, 2 and 4). Mycorrhizal application to transplants improved their performance in a no-tilled rye system (P<0.26) (Fig. 2). In 2001, applying G. intraradices at either sowing or transplanting gave similar results and improved yield on the second harvest date compared to noninoculated plants (P<0.05) (Fig. 4). In both soil types, ‘Terlingua’ onions were higher in yield and soluble solids at harvest, and had larger bulbs, and after 120 days in storage, lost less soluble solids and had less sprouted bulbs compared to ‘1015’ bulbs (Tables 1 and 2). Onions treated with mycorrhizae were more uniform, generally larger in diameter, and stored as well as bulbs from untreated onion transplants. Unsized mean bulb diameters (in mm) from noninoculated plants, or plants inoculated at sowing or transplanting into the Hebbronville soil were 76.8 ± 10.1, 80.2 ± 7.4, and 79.8 ± 6.8, respectively, for ‘Terlingua’, and 72.2 ±