Conservação de sementes de orquídeas tropicais nativas do Oeste Paulista

Abstract

The Orchidaceae family is considered the largest botanical family in number of species, with a wide geographical distribution and having the smallest seeds in the world. To preserve these species in seed banks, many institutions were using tests to evaluate and analyse the physiological quality of the orchid seeds to store and to and ensure the survival of the most endangered species. The objective of this study was to evaluate the germination and seed viability of five native tropical orchid species (Catasetum fimbriatum, Cattleya lundii, Galeandra beyrichii, Macradenia paraensis and Zygopetalum maxillare) from the Morro do Diabo State Park - Teodoro Sampaio-SP. The seeds were conditioned at a water content level (6.4%) and two temperature conditions (20 °C and -18 °C) over six months. The physiological quality of seeds was evaluated before and after storage by tetrazolium tests, germination test and germination speed index, which indicate vigour and viability. A 2x3 factorial design (two temperatures x three storage times) was used with a completely randomized disposition with 3 replications. Data were submitted to analysis of variance (ANOVA, p <0.05), and the mean comparison was made by Tukey test (p <0.05). The species were placed in a growth room with a photoperiod of 16 hours at 25 ± 2 ºC for a maximum of 8 weeks. For Galeandra beyrichii, a terrestrial species, two light conditions were used, germination under lights and in the dark and statistical analysis was performed separately. The results show that storage at 20 °C for 3 and 6 months did not favor C. fimbriatum, G. beyrichii and Z. maxillare, since the first did not germinate at the end of six months and the last two did not germinate in any period. At 20 °C the Z. maxillare species showed loss of viability since the first three months of storage and M. paraensis from the sixth month. However, at -18 °C most species studied germinated better over six months, indicating a better conservation environment. According to the results of the tetrazolium test, the species Catasetum and Cattleya kept the viability rate high at the evaluated temperatures and times, unlike G. beyrichii which in the six months of storage showed a marked loss of viability.