Cultivo in vitro de óvulos de meloeiro

Abstract

The melon (Cucumis melo L.) is a vegetable of worldwide economic importance. The production of dihaploids is a promising alternative to reduce the time to obtain homozygous strains. However, in melon, the efficiency of this method is low, mainly in the stage of regeneration of haploid plants. The in vitro culture of ovules is a way to obtain these haploids. Therefore, the objective of this work was to obtain melon haploid plants by in vitro ovule culture. Ovules of botanical varieties: inodorus, cantalupensis and reticulatus, were excised from flowers with unpollinated ovaries, harvested one day before anthesis, from plants kept in a greenhouse. In the calogenesis step, the ovules were placed in MS + 1.0 μM 6 benzylaminopurine (BAP) and 2.0 μM naphthaleneacetic acid (NAA) for eight weeks at 25 ± 1 ° C, initially in the dark for one week and later in the clear, under photoperiod of 16 hours of light. The design was completely randomized, with each botanical variety being treated with 15 replicates of 10 test tubes (containing two eggs each). At 60 days, callus induction was evaluated in the explants. For aerial part regeneration, calli inodorus and cantalupensis were transferred to the MS + BAP medium at concentrations of: 0.00, 2.22, 4.44, 6.66 and 8.88 μM for 60 days at 25 ± 1 ° C, under a photoperiod of 16 hours of light. The experimental design was completely randomized, in a 2x5 factorial scheme, with two botanical varieties and five culture media, with 10 replicates of five tubes each (one callus per tube). The data were submitted to analysis of variance and the means were compared by the Tukey test at 5% probability. In the histological studies, calli formed from in vitro egg culture were fixed in Karnovsky's solution at days 0, 30 and 60 after inoculation in medium for the induction of calogenesis and at 15, 30, 45 and 60 days after inoculation in means for aerial part regeneration. There was a significant difference for the average callus formation in the three botanical varieties studied. The inodorus variety was the most efficient, producing calluses in 60.65% of the evaluated ovules, differing statistically from the cantalupensis (37.65%) and reticulatus (18.65%) varieties. In the aerial part regeneration phase, there was no bud formation in the media tested for the two varieties. Histological analysis showed presence of starch and formation of conducting vessels, mainly in the callus submitted to the means for aerial part regeneration. Therefore, the protocol used was not efficient to obtain haploid plants of the three varieties of melon studied.