Combined Phosphorus and Water stress Conditions Induce Negative Mycorrhizal Response in Maize (Zea mays L.)

Arbuscular mycorrhizal fungi (AMF) confer both positive and negative effects on the plant symbionts, depending on the prevailing growth condition. We investigated the effect of concurrent variations in phosphorus and soil moisture on percentage root colonization (%RC), mycorrhizal growth response (MGR) and drought response index (DRI) of SAMMAZ-16 maize variety in timescale. The experimental factors were AMF inoculation (addition or no addition), P2O5 applications (30, 60 or 90 kg ha-1) and water regimes (100% and 50% of the soil’s field capacity introduced after 4WAS). The result shows that the overall %RC was 62.22% at 8 weeks after sowing (WAS) and 71.33% at 12 WAS. With 30 and 60 kg P2O5 ha-1 application a rate, %RC was significantly higher at 12 WAS than that of similar application rates at 8 WAS. However, %RC was not different between 8 WAS and 12 WAS in 90 kg P2O5 ha-1 application. AMF inoculation tended to equilibrate the shoot growth of the inoculated plants to that of non- inoculated plants that received 50% higher doses of P2O5 under amply watered conditions. Increasing phosphorus application progressively alleviated the negative mycorrhizal response of the plants at the early stage of growth (week 4) and in 50% FC category at the other sampling times. Higher doses of P2O5 application improved the DRI of the maize in both samplings but the trend was more consistent in AMF-inoculated plants. We conclude that AMF inoculation would be detrimental to the growth of SAMMAZ-16 when there is combined phosphorus and water stress factors