Growth of papaya nodal and rooted shoot cultures as affected by ACC, STS, culture vessel size and incubation conditions

Nodal shoot cultures of 'Clone 003', a selected Australian papaya cultivar, were cultured on modified De Fossard medium supplemented with chemicals that either promote ethylene evolution or inhibit action while in culture. Nodal shoot cultures grown in the presence of 1-aminocyclopropane carboxylic acid (ACC, 1.0 mM) resulted in a significant reduction in percent fresh and dry weights, shoot length, leaf area, petiole length and chlorophyll content, but leaf development was significantly increased. In contrast, nodal cultures grown in the presence of silver thiosulphate (STS, 0.5 mM) significantly produced the highest percentage of fresh and dry weights, shoot length, leaf production, leaf area expansion, petiole length and leaf chlorophyll content. Nodal cultures and rooted whole plantlets placed in medium-sized (125 mL) culture vessels had significantly better growth than those cultures placed in small (70 mL) or in large (250 mL) vessels. Cultures grown in medium-sized vessels had higher fresh and dry weights, longer shoots, more leaves and larger leaf area than those cultures placed in smaller or larger vessels. Similarly, values for said growth parameters and for chlorophyll content of the nodal and rooted whole plantlets were higher when they were incubated under high light intensity of 120 mumol m(-2)s(-1) at a prevailing temperature of either 20+/-1 C or 25+/-1 C

DEVELOPMENT OF CARICA INTERSPECIFIC HYBRIDS

Papaw production in Australia is limited by five major diseases: papaw dieback and yellow crinkle (caused by mycoplasmas); Phytophthora fruit, stem and root rots; black spot (Asperisporium caricae); and papaya ringspot virus-type P (PRSV-P). PRSV-P is the greatest problem for papaya production worldwide and potentially poses the greatest disease threat to the Australian industry. Procedures have been developed to hybridise papaya with related Carica species that are PRSV-P resistant (C. cauliflora, C. quercifolia, and C. pubescens). These procedures may also allow access to other characteristics of wild species eg. Phytophthora resistance (C. goudotiana), high sugar content (C. quercifolia) and cold tolerance (C. pubescens). A highly efficient protocol was developed to rescue and germinate C. papaya x C. cauliflora immature embryos (Magdalita, et al. 1996). Germinated embryos formed embryogenic cultures on hormone free agar solidified medium and multiple hybrid plants were produced. The C. papaya x C. cauliflora hybrids lacked vigour and were generally infertile. Subsequently, the protocol has been adapted to produce hybrids between C. papaya and PRSV-P resistant species C. quercifolia and C. pubescens. Hybrid plants are growing vigorously in the field, and a few C. papaya x C. quercifolia plants have produced some viable pollen. Interspecific hybrid plants have been produced between C. papaya, and C. goudotiana and C. parviflora. C. parviflora has been hybridised with C. pubescens and C. goudotiana. Plants of all crosses are growing in the glasshouse or field

Effect of medium replenishment and acclimatization techniques on growth and survival of embryo cultured coconut seedlings

The effect of different media replenishment or in vitro irrigation techniques on seedling growth of ‘Laguna Tall’ coconut seedlings in vitro was studied. Likewise, the effect of in vitro acclimatization techniques using polyethylene glycol and polyvinylpyrolidone on growth and survival of coconut seedlings after acclimatization was investigated. In addition, the effect of three ex vitro acclimatization techniques and potting-out at two different stages of seedling growth on the survival and growth of coconut seedlings was studied. Replenishment of the medium or in vitro irrigation every 60 days and regular subculture every 30-40 days significantly promoted plant height and development of secondary roots. The two in vitro irrigation techniques significantly decreased the percent contamination of cultures. Polyethylene glycol (PEG, 10 and 20 mg L-1) and polyvinylpyrolidone (PVP, 10 and 20 mg L-1) significantly reduced the number of secondary roots and expanded leaves in vitro and the plant height and leaf production ex vitro. Acclimatization using the plastic tent and the wooden box humidity chamber gave higher seedling survival than the T misting method. Furthermore, potting-out at two different stages of seedling development (i.e. two- and three-leaf stage) did not significantly affect growth and survival of seedlings after acclimatization

Effect of physical, chemical and light treatments on germination and growth of tissue-cultured coconuts

The acclimatization and ex vitro establishment of tissue cultured coconut plantlets regenerated either from zygotic or somatic embryos could result to serious losses. Although high germination rates can be achieved in vitro, the survival of zygotic embryo derived plantlets in soil is very low (0-30%). Hence, treatments that could promote development of good quality seedlings having well-developed shoot and root is needed to increase seedling survival ex vitro. The effect of physical, chemical and light quality treatments on germination and growth of coconut embryos and tissue-cultured seedlings respectively, was investigated. The germination of coconut embryos was promoted when placed in a liquid Euwens (Y3) medium and incubated using a roller drum. Gibberellic acid (GA3) significantly affected growth of seedlings as it promoted shoot elongation, shoot and root expansion, and fresh and dry weight increase. However, GA3 did not significantly affect germination. In addition, the blue, red and yellow light significantly affected growth of seedlings as it promoted leaf and shoot elongation, fresh and dry weight increase, and root and leaf production. These conditions could be used to improve the growth and survival ex vitro of tissue cultured coconuts

An efficient interspecific hybridisation protocol for Carica papaya LxC cauliflora Jacq.

A protocol for interspecific hybridisation between Carica papaya and C. cauliflora is necessary for gene introgression between these 2 incompatible species. Carica papaya x C. cauliflora hybrids were successfully created using a new, efficient hybridisation protocol. This protocol includes the use of highly viable pollen of C. cauliflora produced during summer, autumn and/or spring, the use of an isolation time ranging from 90 to 120 days post-pollination of hybrid embryos, and the use of the most compatible C. papaya cultivar 2001 for crossing with C. cauliflora. Two types of interspecific hybrid embryos, namely single and multiple, were isolated in all resulting fruit. The application of gibberellic acid (0.6 or 0.8 mol/L) or 2,4-dichlorophenoxyacetic acid (1.5 or 2.0 mol/L) to freshly cross-pollinated flowers and pollination by mentor pollen did not promote either the rate of successful crosses or the production of hybrid embryos. Using this efficient protocol, hybridisation between C, papaya and C. cauliflora conducted in 3 locations in south-east Queensland produced 338 crosses which generated 43 736 seed. From these seed, 2100 hybrid embryos were recovered resulting in the production of 485 morphologically normal interspecific hybrid plants. Studies reported elsewhere show that these hybrids are resistant to papaya ringspot virus type P

Morphological, molecular and cytological analyses of Carica papaya x C-cauliflora interspecific hybrids

Morphological, molecular and cytological analyses were performed to assess the hybridity of 120 putative interspecific hybrids of Carica papaya L. x C. cauliflora Jacq. In the putative interspecific hybrids the number of main leaf veins was intermediate between the two parents while the hermaphrodite flower sex form and the low vigour were distinctive features of these hybrids. Petiole length, stem diameter, leaf length, leaf width and flower colour were similar to C. papaya, whereas leaf shape, type, serration, venation, petiole hairiness and flower shape were similar to C. cauliflora. Markers generated by the polymerase chain reaction using 72 10-mer primers (random amplified polymorphic DNA) revealed a high level of polymorphism (64%) between C. papaya and C. cauliflora. Seventeen of these primers yielded reliable and easily scorable polymorphic banding patterns that were further screened to reveal hybrids. A range of 1-5 RAPD primers consistently confirmed that all 120 plants were genetic hybrids, with all of them containing at least one band from the male parent. Cytological analysis revealed that 7-48% of the cells in many of the interspecific hybrids were aneuploid suggesting that chromosome elimination was occurring. The frequency of aneuploid cells was negatively associated (r = 0.88) with the number of bands from the male parent integrated into the hybrid. Pollen fertility of the hybrids was from 0.5 to 14.0% while C. papaya and C. cauliflora had 88.0-99.0% and 90.0-97.0% fertile pollen, respectively