The effect of inoculation of potato (Solanum tuberosum L.) microplants with arbuscular mycorrhizal fungi on tuber yield and tuber size distribution

Potato microplants were inoculated with three commercial arbuscular mycorrh izal inoculants, Vaminoc (MicroBio, Hemel Hempstead, HP2 7SU, UK), Endorize IV and Glomus intraradices (both produced by Societe Biorize, 21000 Dijon, France) at establishment ill the glasshouse. Monitoring of percentage root length colonization confirmed the persistence of all the mycorrhizal fungi during the trial. Colonization with Vaminoc and Endorize IV levelled-off a t approximately 8 weeks and with G. intraradices at 12 weeks. Image analysi s of leaf shape parameters at 4 weeks in the field indicated that the contr ol uninoculated :microplants and the microplants from the Vaminoc treatment were significantly the most mature of the microplant-derived populations. Microplants from the Endorize IV treatment were significantly less mature t han from the Vaminoc treatment and those from the G. intraradices treatment significantly the least mature. The G. intraradices treatment was late flo wering. The Vaminoc and Endorize treatments promoted flowering, 80 and 76%, respectively, at 2 months after planting, relative II, the microplant cont rol (60% at 2 months), the G. intraradices treatment reduced flowering, 14% at 2 months. Mycorrhizal dependency determined at harvest showed that Vami noc and Endorize IV promoted growth relative to the control whereas G. intr aradices reduced growth. Average tuber yield for a seed-tuber-derived contr ol was 1.2 kg per plant, and the average yield per plant for the microplant control was significantly lower at 0.9 kg. The Vaminoc treatment was not s ignificantly different from the microplant control. The Endorize TV and G. intraradices yields were significantly lower at 0.64 and 0.41 kg per plant, respectively. Since the objective was to evaluate the potential of mycorrh izal fungi to improve yield of seed grade tubers from microplants, tuber si ze distribution was analysed. The average number of seed grade tubers for t he respective treatments were, 1.2 for the seed-tuber crop, 3.8 for the con trol microplants, 3.8 for the G. intraradices, 6 for Vaminoc and 8.5 for En dorize IV crops, respectively. It has been shown here that mycorrhizal inoc ulation can influence the yield quality of potato microplants. These result s support previous findings that mycorrhizal fungi can increase or decrease yield depending on the mycorrhizal isolate and host genotype. Leaf image a nalysis has been shown to have predictive value in evaluating the potential of mycorrhizal treatments. The determinants of tuber yield and tuber size distribution in potato are complex and results, such as those obtained here , would require to be repeated in multiple sites and successive years to co nfirm the stability of the interactions reported. (C) 2000 Elsevier Science B.V. All rights reserved.