Screening for Low-Phosphorus Tolerance and Mycorrhizal Responsiveness Among Tomato Strains

Abstract

The studies were carried out in order to identify tomato strains (Lvcopersicon esculentum) tolerant to low available phosphorus in soil and to determine effect of vesicular-arbuscular mycorrhizal fungi (VAMF) on tomato strains. Low-P tolerance was identified from the comparison of growth under low (P deficient) and high P (P sufficient) conditions. Strains with negligible growth reduction under low P condition were considered low-P tolerant. Two methods (sand-soil pot and field methods) were used to screen for low-P tolerant tomato strains. Strains 15, 20, 50, 51, 55, 58, 59, 60, 68, 69, 159 and 214 were identified as the potential low-P tolerant strains in sandsoil pot study. Strains 43, 59 and 999 were selected as the low-P tolerant strains in field study. In order to evaluate how well conclusions drawn from different screening methods correlate with field results, the low-P tolerant screening results from the sand-soil study, a root liquid culture experiment (Coltman, 1987), and a sand-alumina study (Coltman et al., 1985) were all compared to the field results. The results of screening the low-P tolerant tomato strains in the sand-alumina system (Coltman et al., 1982) and root liquid culture method (Coltman, 1987) were not significantly correlated with the field study. Screening for low-P tolerance in the sand-alumina and the root liquid culture systems, therefore, can not substitute for field screening studies. However, the sand-alumina system did show potential to screen strains for high P utilization efficiency. Plant growth and P uptake were correlated significantly between the sand-soil and field studies. Sand-soil studies appeared to have good potential to substitute for field studies in screening for low-P tolerant tomato strains. Inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) decreased P uptake and plant growth in the sand soil study. In this study, plant were analyzed after only 24 days of growth, and the time was probably too short to allow mycorrhizal symbiosis to increase plant P uptake. This early growth depression was possibly due to VAMF competing for nutrients with the host plants. In the field study, plants were analyzed after 85 to 100 days of growth. In this period of time mycorrhizal symbiosis became established, and increased P uptake in some strains more than 100%. Strains benefitting most from VAMF inoculation tended to have low p uptake ability. However, not all strains which had low P uptake ability benefitted from the mycorrhizal symbiosis. Therefore, the presence or absence of mycorrhizae should be considered when making recommendations on low-P tolerant strains.