Production of haploid embryos and plants in Iranian melon (Cucumis melo L.) through irradiated pollen-induced parthenogenesis.

The irradiated pollen technique (IPT) is the most successful haploidization technique within Cucurbitaceae. The influence of gamma-ray doses (250, 350, 450 and 550 Gy), genotypes and stage of development of embryos obtained by IPT on the induction of haploid embryos were studied in several Iranian melon cultivars as well as their hybrids with alien cultivars. Female flowers were pollinated using pollen that had been irradiated with gamma rays. Different shapes and stages of embryos were excised 21-25 days after pollination and cultured on E20A medium. Direct culture, liquid culture and integrated culture methods were used; integrated culture and liquid culture methods showed advantages in increasing the efficiency of haploid plant production in melon breeding programmes. Results revealed that 550 Gy of gamma irradiation was successful in inducing parthenogenesis and fruit development, whereas lower irradiation doses were not effective in inducing haploid embryos. The percentages of embryos per seed were the highest in 'Samsoori' (1.2%) and 'Saveh' (1.1%) cultivars. Some of the heart-shaped and cotyledon-shaped embryos developed into haploid plants. In total, 52 parthenogenic melon plantlets were recovered from 274 embryos via IPT. Production of haploid embryos and haploid plants was strongly influenced by gamma-ray dose, embryo stage and genotype. Indirect methods and chromosome counting performed on the root cells of regenerated plants showed that these plants were haploid (n = x = 12).

Effect of gamma ray irradiated pollen technique on seed development pattern in Citrus

In modern fruit breeding, to reduce the breeding cycle, induction of haploid plants through irradiated pollen technique is of paramount importance. However, the major drawback is the sensitivity of pollen to higher irradiation doses as it induces abnormality in double fertilization process. Hence, optimization of irradiation doses for maximum recovery of healthy seed is very important. Present work analyzed the seed developmental pattern of Citrus grandis, pollinated with gamma irradiated pollen (100-500 Gy) of C. limon, C. limetta, and C. sinensis. Not a single fruit was retained on the tree till maturity in C. grandis × C. limon crosses; however, in other two cross combinations, fruits were harvested at maturity only up to 300 Gy irradiation doses. Among the harvested fruit, normal seed decreased gradually with increasing irradiation doses and less than 5 normal seeds per fruit were obtained at 300 Gy with maximum in C. grandis × C. limetta cross. However, abnormal and empty number no. of seeds has increased significantly with increasing irradiation doses. Developmental pattern of embryo and endosperm within normal seeds was also influenced significantly by irradiation treatment. At higher doses, seeds number with both embryo and endosperm was decreased gradually and at 300 Gy, it was reduced to 59.47% as compared to control.

Production of callus mediated gynogenic haploids in winter squash (Cucurbita maxima Duch.) and pumpkin (Cucurbita moschata Duch.)

Although haploids were successfully produced via irradiated pollen technique and anther culture in Cucurbita maxima and Cucurbita moschata, the haploidization efficiency is still low due to genotype dependence. Thus, as an alternative technique, the efficacy of the ovule culture was investigated. Ovules were extracted at different flowering time and then cultured on a solid MS medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D), benzylaminopurine (BAP), thidiazuron (TDZ), and naphthaleneacetic acid (NAA) to induce callogenesis and plant regeneration. The gynogenic response was influenced by the combination of plant growth regulators, genotype and culture time. The medium containing of 4.0 mg/l BAP + 0.05 mg/l NAA + 0.1 mg/l TDZ provided the highest response at anthesis time. Plantlets were rooted and elongated on a solid MS medium supplemented with 0.01 mg/l indole-3-acetic acid (IAA) + 1.0 mg/l BAP. The ploidy observations of 122 plants revealed that 70 plants were haploid, 46 plants were diploid and the others were mixoploid.

No Effect of Seed Presence or Absence on Sugar Content and Water Status of Seeded and Seedless Watermelon Fruits

We investigated physiological differences in watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] fruits among seeded diploid and seedless triploid fruits, N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU)–treated seedless fruits, and soft-X–irradiated pollen-pollinated seedless fruits to investigate the effect of the presence or absence of seeds on water relations and sugar content. We picked fruits at 20 and 40 days after anthesis and sampled flesh at the center, around the seeds, and near the pericarp to measure water status and sugar content. There were no significant differences between seeded and seedless cultivars in sugar contents or in water and osmotic potentials of the flesh, although the latter two were decreased at 40 days. CPPU and soft-X–irradiated pollen eliminated mature seeds, but there were again no significant differences in sugar contents or water status between seeded and seedless fruits. Thus, the presence or absence of seeds did not influence the sugar content or osmotic pressure in watermelon fruit, so sugar accumulation was not related to seeds.