Phosphorus is the most important element to plant nutrition. Mycorrhiza has the capability to improve plant yield by increasing plant nutrient supply. Hence, we studied the effect of presence and absence of mycorrhiza on growth and productivity of summer squash under different phosphorus levels (0, 25, 50, 75 and 100 kg ha-1) as a factorial based on randomized complete block design. Results showed that with increasing phosphorus fertilizers, fruit number per plant was increased, but seed number per fruit decreased. In addition, mycorrhiza inoculation with application of 50 kg ha-1 phosphorus fertilizer had maximum values for root colonization (54.33%), oil (45%) and linoleic acid (68.25%) percentage. So, probably mycorrhiza is a good substitute for phosphorus fertilizers. Mycorrhiza symbiosis had a direct relationship with summer squash yield. Therefore, it seems that the low rate of phosphorus fertilizer application, leads to improved interaction with mycorrhiza.
