Effect of gamma ray irradiation and cryopreservation on pollen stainability, in vitro germination, and fruit set in Citrus

Abstract

The present work analyzed the stainability and in vitro germinability of the gamma-ray-irradiated fresh and cryopreserved pollens of 3 Citrus species: C. limon, C. limetta, and C. sinensis. Fruit set after pollinating 75 flowers of C. grandis with irradiated and nonirradiated (control) fresh and cryopreserved pollen was also assessed. Results showed that in solid and liquid culture media the highest in vitro germination values were detected in fresh (61.45% and 62.53%, respectively) as well as cryopreserved (53.17% and 55.36%, respectively) C. sinensis nonirradiated pollens. However, at a higher irradiation dose of 500 Gy in both culture media, the minimum reduction of germinability of fresh (30.85% and 28.01%) and cryopreserved pollens (33.37% and 31.06%) was found in C. limon. Contrary to in vitro germination, the minimum reduction in stainability of fresh and cryopreserved pollens, as assessed by acetocarmine (9.51% and 11.85%, respectively) and FDA tests (10.78% and 12.73%, respectively), was recorded in C. limetta. Regardless of irradiation dose, the highest fruit setting in C. grandis at 40 days after pollination was detected when it was pollinated with both fresh (38.02%) and cryopreserved (34.92%) C. limetta pollen grains.

Viabilidad y longevidad del polen en genotipos de limón mexicano estimada mediante germinación in vitro

“…La viabilidad del polen y su poder germinativo en laboratorio se puede determinar mediante a): Pruebas de germinación in vitro (Moura et al, 2015;Shekari et al, 2016); b) medición de la actividad enzimática (Gozlekci et al, 2011;Soares et al, 2013;Demir et al, 2015); y c) la tinción del citoplasma del grano de polen (Maiti y Rodríguez, 2015;Baswal et al, 2015). Sin embargo, Soares et al (2013); Kundu et al (2014); Shekari et al (2016), coinciden que la germinación in vitro es más confiable ya que los métodos de tinción pueden sobreestimar la viabilidad del polen. Por otra parte, la longevidad del polen, considerada como el período de tiempo durante el cual el polen mantiene su viabilidad, es decir, la capacidad de germinación y de fertilización, varía mucho con las especies de plantas y las condiciones de almacenamiento (Dafni y Firmage, 2000).…”

Induction of haploid plants in citrus through gamma-irradiated pollen and ascertainment of ovule age for maximum recovery of haploid plantlets

“…However, ovule cultures at 50 DAP gave the highest frequency of embryoid formation, embryo germination, and plantlet regeneration, which was significantly higher than ovule culture at 20 and 35 DAP. The fertilization process within the ovules of citrus started only after 25 DAP (Kundu et al, 2014), and after fertilization, it may take some more days to develop the embryo within the ovules. Hence, ovules cultured at 20 DAP following pollination with irradiated pollen may be devoid of fertilized embryos, resulting in a very low frequency of embryoid formation and degeneration of those embryoids at early stages before their germination, which ultimately caused a very low rate of embryo germination and plantlet regeneration.…”

“…Thereafter, emasculation and pollination of those selected flowers were carried out with irradiated pollen grains having viability of 89.06% and 78.26%, respectively, for nonirradiation and 400 Gy irradiation treatment, irrespective of the pollen parent (Kundu et al, 2016). Thereafter bagging and labeling was done according to the method described by Kundu et al (2014).…”

“…Based on our previous year's study on the standardization of gamma ray irradiation doses and pollen parents for pollen viability, fruit set (Kundu et al, 2014), and seed development in citrus, two Citrus species, sweet orange (Citrus sinensis (L.) Osb. 'Mosambi') and sweet lemon (C. limetta Risso), were selected as pollen sources for the experiment.…”

“…The irradiation of pollen grains was performed at 50, 100, 200, 300, and 400 Gy by cobalt 60 gamma rays (NRL, IARI, New Delhi, India) according to the method described by Kundu et al (2014). Twenty unopened flowers (for each exposure) approaching anthesis were separately collected from the above two Citrus species selected as pollen parents, in the morning (0900 to 0930 hours).…”