Influence of arbuscular mycorrhizal inoculation and humic acid application on growth and yield of Roselle (Hibiscus sabdariffa L.) and its mycorrhizal colonization index under deficit irrigation

In this study effect of irrigation managements including irrigation after 100 and 200 mm pan evaporation as normal and deficit irrigation respectively was investigated in Roselle plants. Effects of humic acid (including 0 and 4 kg ha-1) and mycorrhizal inoculants (including Glomus versiforme (GV) and Rhizophagus irregularis (RI)) were also studied on growth, yield and mycorrhizal symbiosis index of Roselle plants. Drought stress reduced the amounts of morphological indices and yield components, while mycorrhizal treatment particularly RI inoculation and to a lower extent humic acid application reduced the negative impacts of water deficit on growth and yield of Roselle plants. Both inoculants of mycorrhizal fungi increased the economical yield of Roselle under drought stress condition, where the amount of calyx yield for RI, GV and control in 200 mm pan-evaporation treatment was 130, 127 and 66 kg ha-1, respectively. In addition, the highest root mycorrhizal frequency was obtained at normal irrigation × humic application × RI (95%) and the lowest value was observed at deficit irrigation × no-humic × no-mycorrhizal inoculation (31.6%) treatment. In conclusion, combined effects of experimental factors showed that seed inoculation of plants by mycorrhiza and to some extent application of humic acid are two reliable strategies for Roselle production under deficit irrigation