Floralcharacterization, pollen grain description, viability, germination andproductive performance of Castanea crenataSiebold & Zucc (Fagaceae) in tropical regions

Abstract

The genus Castanea Mill., is comprised of ten species; monoecious trees with staminate and androgynous catkins of varying sizes. Originating from China, chestnuts are distributed widely around Asia, Europe and all around the world. The chestnut tree has multiple purposes, ranging from use in gastronomy to the manufacture of utensils since the fruit does not have gluten and has good quality protein. The domestication of the genus is still in process since world production still counts on natural chestnut trees and large-scale production requires homogeneous plantations. Studies such as floral biology, pollen grain fertility and productivity can provide support for other programs and thus contribute to obtaining these homogeneous plants. With the demand in the food market, it is necessary to increase production and invest in more sustainable means. Most studies of the genus are focused on the species Castanea sativa Mill., as it is more commonly known and produced, leaving studies on other species mostly disregarded. The objective of this work was to present the floral characterization of the species Castanea crenata Siebold and Zucc., develop a germination protocol for the cultivars of the genus, verify the pollen viability through colorimetric tests, classify the pollen grain and point out the most suitable cultivars for production in tropical regions. For floral characterization, development of the germination protocol, evaluation of pollen viability and pollen grain classification, nine cultivars of C. crenata and two hybrids (C. crenata x Castanea sp) were used. The material was collected at Chestnuts from the Sustainable Rural Development Coordination - CDRS, in São Bento do Sapucaí-SP and the fixed material was prepared at the Cytogenetics Laboratory of the Federal University of Lavras-MG. The flowers were characterized by observation of the floral parts. The use of literature and germination was obtained through tests of culture media. Pollen viability was assessed using two dyes, Carmine Propionic and Alexander Dye. Pollen grains were classified as viable and non-viable. To describe the pollen grain, the acetolysis technique was applied and the grains were classified according to Erdtman (1943). In the productivity experiment, four cultivars of C. crenata were used and conducted at the Experimental Unit of the Orchard of the Federal University of Lavras-MG, the collections were carried out over four harvests. The inflorescences of the species C. crenata, are of the type staminate or androgynous, where the female flowers are located at the base of the male flowers. The best culture medium in which pollen tube germination was provided was 6 g L-1 of agar, 46.5 g L-1 of sucrose and 460.23 mg L-1 -1 of boric acid in the absence of nitrate. Calcium, pH 5.25 where germination reached 30% and the cultivars indicated to be donors of pollen grains were ‘Morioase’ and ‘Tamatsukuri’. The pollen grains were classified as prolate, isopolar, tricolporate, with long constricting colostrum, heteroapertured, zonocolporate and with exine smooth. Pollen viability indicated that the cultivar ‘Morioase” has the highest rate of viable grains. As for productivity, the studies indicated that the cultivars ‘Taishowase’ and ‘Okuni’ are the most promising for cultivation in tropical regions.