Applied Soil Ecology 15 (2000) 137–144 The effect of inoculation of potato (Solanum tuberosum L.) microplants with arbuscular mycorrhizal fungi on tuber yield and tuber size distribution Elizabeth M. Duffy, Alan C. Cassells ∗ Department of Plant Science, National University of Ireland, Cork, Ireland Received 31 May 1999; received in revised form 9 December 1999; accepted 23 March 2000 Abstract Potato microplants were inoculated with three commercial arbuscular mycorrhizal inoculants, Vaminoc (MicroBio, Hemel Hempstead, HP2 7SU, UK), Endorize IV and Glomus intraradices (both produced by Societe Biorize, 21000 Dijon, France) at establishment in 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 at approximately 8 weeks and with G. intraradices at 12 weeks. Image analysis of leaf shape parameters at 4 weeks in the field indicated that the con- trol 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 than from the Vaminoc treatment and those from the G. intraradices treatment significantly the least mature. The G. intraradices treatment was late flowering. The Vaminoc and Endorize treatments promoted flowering, 80 and 76%, respectively, at 2 months after planting, relative to the microplant control (60% at 2 months), the G. intraradices treatment reduced flowering, 14% at 2 months. Mycorrhizal dependency determined at harvest showed that Vaminoc and Endorize IV promoted growth relative to the control whereas G. intraradices reduced growth. Average tuber yield for a seed-tuber-derived control was 1.2 kg per plant, and the average yield per plant for the microplant control was significantly lower at 0.9kg. The Vaminoc treatment was not significantly different from the microplant control. The Endorize IV and G. intraradices yields were significantly lower at 0.64 and 0.41kg per plant, respectively. Since the objective was to evaluate the potential of mycorrhizal fungi to improve yield of seed grade tubers from microplants, tuber size distribution was analysed. The average number of seed grade tubers for the respective treatments were, 1.2 for the seed-tuber crop, 3.8 for the control microplants, 3.8 for the G. intraradices,6 for Vaminoc and 8.5 for Endorize IV crops, respectively. It has been shown here that mycorrhizal inoculation can influence the yield quality of potato microplants. These results support previous findings that mycorrhizal fungi can increase or de- crease yield depending on the mycorrhizal isolate and host genotype. Leaf image analysis 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 ∗ Corresponding author. Tel.: +353-21-4902726; fax: +353-21-4274420. E-mail address: a.cassells@ucc.ie (A.C. Cassells) 0929-1393/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0929-1393(00)00089-5