Seasonal dynamics of root morphology and mycorrhizal colonization in terrestrial orchid Habenaria longicornu Lindl., Southern India

The present investigation assesses how seasonal changes and developmental stages influence root hair characteristics and mycorrhizal colonization in terrestrial orchid Habenaria longicornu . The root hair number, root hair breadth, cell length, cell breadth and peloton length showed marked seasonal differences, whereas root hair length and peloton breadth were largely unaffected by season, orchid seedling stage and both of its interactions. But the positive relationship has been observed between cell length and peloton length. The degrees of mycorrhizal colonization showed that 88% during November with significant seasonal as well as season-stage interaction. Root length with degenerating pelotons was 72% whereas intact pelotons were 8% and showed significant seasonal variations. Root hair numbers were positively correlated with total mycorrhizal colonization. The distribution of colonized and uncolonized cells in the cortical regions showed significant seasonal variations. The highest intact to lysed peloton ratio 0.49 during the mature vegetative stage in July while 0.38-0.40 during December and the seasonal variations were significant. These observations clearly showed dynamic interplay between root hair morphology and orchid mycorrhizal colonization highlighting the crucial role of seasonality in shaping symbiotic association in terrestrial orchids.