Analyses of the sexual reproductive traits for conservation and sustainable utilization of Dactylorhiza hatagirea – A critically endangered medicinal orchid of North-western Himalaya

Abstract

To undertake scientifically appropriate management and conservation practices, understanding the reproductive biology of endemic and threatened species is critical. Dactylorhiza hatagirea is an important medicinal plant whose reproductive strategies and adaptive evolution mechanisms are still not fully clear. The present study was conducted in the North-western Himalaya of India to understand the reproductive biology, breeding system and pollination ecology of D. hatagirea; an endemic and critically endangered orchid. It is a perennial herb that grows along the altitudinal gradients of 2100–3107 m.a.s.l. and overcomes harsh winters through underground perrenating tubers. The flowering commences from May to July and the flowers are completely zygomorphic with male and female reproductive organs fused to constitute gynostemium. Analysis of variance (ANOVA) show significant statistical difference (p < 0.05) between the floral traits for most of the characters. Each flower bears two dark green colored pollinaria with an average of 212.14 ± 14.4 pollinia. Pollen occur as tetrads and polyads in massulae and their viability was greater than 95 ± 4.2 %. Stigma receptivity was confirmed on the day of anthesis and reaches its peak on 5–6th day. Cruden outcrossing index (5), asynchronous anthesis, conspicuous inflorescences, nectaries, presence of rostellum and herkogamy points towards outcrossing nature while pollen ovule ratio (1.27 ± 0.4) and the greater value of self-incompatibility (0.9) reflect that plants are potent cross-breeders. Pollination treatments significantly impacted seed set in D. hatagirea (one-way ANOVA; F = 23.14; p = 0.001) with an average seed set of 92.75 % ± 0.95 for manual xenogamy (p < 0.01), 89.5 % ± 2.38 for geitonogamy (p < 0.01) and 17 % ± 2.2 for bagged inflorescences (p<0.05). Pollination syndrome is exclusively entomophilly. Insignificant difference was reported in the timining for the insect visitation to flowers (calculated value = 3.4; critical value = 5.1; p < 0.01), however different environmental factors created a significant impact on the frequency of insect visitation (calculated value = 9.7; critical value = 4.3; p < 0.01). Apis cerana, Apis mellifera and Bombus asiaticus show highest pollination indices (p < 0.01) and were characterized as dominant pollinators. This study provides a detailed explanation and substantial understanding regarding operative reproductive mechanism of this threatened medicinal plant and can be used by conservation biologists to develop holistic and effective conservation strategies and address the unique challenges that this threatened species face in the wild.