(carica papaya l.) - a review

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Agri. Review, 35 (4): 307 - 313, 2014 doi:10.5958/0976-0741.2014.00919.2

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ASPECTS ON ASEXUAL PROPAGATION IN PAPAYA (CARICA PAPAYA L.) - A REVIEW S. Senthilkumar* , N. Kumar1, K. Soorianathasundaram and P. Jeya Kumar2

Received: 15-11-2013

Department of Fruit Crops, Tamil Nadu Agricultural University, Coimbatore-641 003, India.

`

Accepted: 17-11-2014

ABSTRACT

Papaya is one of the few important fruits which flowers and yield throughout the year. Though a polygamous species with three basic types viz., staminate, pistillate and bisexual, its cultivation with seed propagation is hindered by problems due to wide variability in sex expression and fruit characters even in small population of dioecious cultivars. In such point of view, propagation through asexual method could be a better alternative. This substitute method of propagation by cutting or grafting would be of great boon to papaya industry. This review summarizes the documented approaches made so far to overcome the constraints of inherent heterozygosity, dioecious nature and susceptibility to a large number of viral diseases by means of vegetative propagation in papaya.

Key words: Asexual propagation, Dioecious nature, Performance of grafts, Variability with seedlings. The importance of papaya to world’s economy is demonstrated by its wide distribution, substantial production in the tropical countries, besides its high nutritive value. It has long been grown and cultivated in the home gardens by the people of tropics, as it adapts itself to diverse soil and climatic conditions. The total area occupied by papaya in India is estimated around 1,17,400 ha (NHB, 2012). It is extensively grown in the states of Andhra Pradesh, Tamil Nadu, Assam, Bihar, Maharashtra, Uttar Pradesh, Gujarat, Punjab, West Bengal, Madhya Pradesh, Karnataka etc. It is largely consumed locally although it has huge potential for export. Propagation by seed is the most practical method in papaya (Hartmann and Kester, 1975). But, the plants grown from seeds of open pollinated flowers result in a mixture of genotypes, with considerable variation in disease susceptibility, fruit quality and yield (Saker et al., 1999). In dioecious cultivars of papaya, equal probability of male and female plant population poses the problem of rouging excess male plants. In the case of gynodioecious cultivars, the bisexual types which produce oblong fruits are preferred to round fruits of female plants

as they fetch premium price in the market. Vegetative propagation method can be an alternative to seed propagation to overcome these constraints. Generally, plants produced through vegetative propagation are known to be true to type in preserving the genotype of cultivars in any crop. Seedling variability in papaya: Propagation of the papaya for commercial production is normally by seed; as a consequence, wide variability in sex expression and fruit characters are usually observed among the individuals in the population of even small plantings, which poses problems in breeding and selection (Sookmark and Tai, 1975). Seed propagation in papaya leads to the occurrence of undesirable genetic variations due to open pollination, resulting in a mixture of genotypes. Além de problemas na germinação, pela ocorrência de substâncias inibidoras presente no arilo, a extração ea conservação das sementes ainda precisam ser melhor estudadas, uma vez que as sementes podem perder o poder germinativo em períodos relativamente curtos (Couto, 1983). In addition, the occurrence of inhibitory substances present in the aril, extraction and conservation of seeds may cause

*Corresponding author’s e-mail: [email protected], 1Department of Spices and Plantation Crops, Tamil Nadu Agricultural University, Coimbatore-641 003, India., 2Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore-641 003.

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germination loss in relatively short periods (Couto, 1983). According to Marin and Silva (1996), the possibility of maintaining original characteristics of the parent plants of papaya does not occur in the conventional system of production where seeds are harvested in majority of cases, from commercial open pollinated orchards. Teixeira et al. (2009) reported papaya propagated through seeds produce plants with considerable variation in sex types (a mix of male, female and hermaphroditic plants) which is highly undesirable that results in variation in fruit quality and type. Asexual propagation: One advantage of asexual propagation is that the sex is known. In dioecious lines, all productive plants are female and only a few male plants, raised from seed or cuttings, are required for pollination. San Jose and Marim (1988) reported the possibility of developing materials highly productive and resistant to viruses, which can be spread safely keeping intact the characteristics of the mother plants of papaya through asexual propagation. According to Reuveni et al. (1990) the clonal propagation technique of selected mature female and male plants in papaya is highly desirable for commercial practice, especially in subtropical areas, as the dioecious lines exhibit considerable variation in shape, size and flavor of the fruit and disease susceptibility. Thus by vegetative propagation, there is a possibility of maintaining the original characteristics of the parent plant apart from several advantages like higher yield, lower fruiting height, longer cropping span.

Singh et al., (1986) found that patch budding consistently gave a higher percentage of success over shield budding. The latter is not recommended since the papaya rootstock bark cannot be easily lifted for insertion of bud. Vegetative propagation of the superior papaya clone ‘Honey Gold’through leafy cuttings and grafting has been practiced successfully for over 25 years at South Africa. Clones that are adapted to local conditions were selected and propagated vegetatively in other areas. These vegetatively propagated plants could be kept in production for a longer time than seedlings (Allan, 1995).

Propagation by grafting in papaya: The purpose of propagation by grafting is the maintenance of desirable traits. Due to the example of the work developed, the technique of grafting can be applied in the culture of papaya. Grafting has been used by Jimenez (1957) among six species of papaya by apical wedge grafting method with the intention of producing a combination of periclinal chimeras of C. papaya and C. cauliflora. All the combinations were compatible and produced vigorous plants. Grafting and inarching of promising papaya hybrids and inbreds onto C. cauliflora, a wild resistant to PRSV-P was found to delay the symptom expression in papaya (Villegas et al., 1997). Ramkhelawan et al. (1999) conducted studies to develop simple methods of propagation of papaya in vivo, thus providing growers a wide choice in methods of production of standard varieties. Among various propagation methods, terminal wedge grafting was Propagation methods tried in papaya: Screening clearly superior to the chip budding and side grafting, of several works shows that vegetative propagation with success rates of 100%, 85% and 75% methods such as cuttings and grafting have been respectively and good growth performance in the successfully adopted in papaya. A work in field. The effect of grafting on the fruiting of Tainung propagation by cuttings of papaya were initiated by No. 2 and Tainung No. 5 papaya varieties revealed Allan (1964) to eliminate the variability in certain that grafted plants had a tendency of being shorter clones, so that, their performance could be more than ungrafted seedlings; they did not show accurately compared in evaluation studies. These incompatibility between scion and rootstock and studies were performed with the clones ‘Hortus yielded better than ungrafted papaya trees (Weng Gold’and ‘Honey Gold’, the latter being obtained and Yang, 1999). Nhat Hang and Chau (2000) from the first selections reaching higher standard and reported the effect of rootstocks on growth, is resistant to anthracnose. Theakston (1976) development and fruiting of cv. Trang Nguyen on six reported treating the papaya cuttings with IBA, papaya varieties selected as rootstock. The results applied at the base, produced satisfactory results in showed that top grafting on Papaya LD-1999 gave the induction of roots. Plants obtained by cuttings the highest percentage of survival (83.91% and fruited earlier compared to plants obtained by seed. 75.15%). Both Papaya LD-1999 and Kaegdum

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varieties gave significantly shorter seedlings than the control. Phenology and production of Carica papaya ‘Honey Gold’under cool subtropical conditions were reported by Allan (2007). Vegetative propagation of selected, red fleshed hermaphrodite types ensured the production of fruits of outstanding quality for discerning markets. Chong et al. (2008) reported the grafting success (about 80%) through cleft method in ‘Eksotika’papaya at nursery stage. They stressed the advantage of grafted papaya trees as they bear fruits much lower and earlier and are dwarf in stature with longer economic life cycle. There is also potential in utilizing rootstocks for tolerance to ‘wetfeet’and soil-borne diseases. A better approach of obtaining 100% hermaphrodite stand by cleft grafting papaya seedling using healthy disease free scions was suggested by Chong et al., (2005). Allan et al. (2010) reported the higher percentage of success (80%) by side grafting obtained after 15 weeks on the vigorous, well fertilized stocks surface sterilized with 10% sodium hypochlorite. Moreover, the surface sterilization with household bleach controlled the bacterial rot of scions. In an evaluation study, the efficiency of grafting as a method of multiplying papaya vegetatively, cleft grafting exhibited complete success (100%) (Anonymous, 2010).

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small, pencil-sized side shoots. Allan et al. (1993) demonstrated that Promalin (BA + GA4+ 7) promoted more spindle shoots, while CPPU + GA3 caused new leaf and stem distortion initially, but subsequently produced normal shoots. However, for plants treated in autumn, complete leaf removal had detrimental effect on plant survival, whereas plants with growing point cut out, but with the older leaves retained, continued producing many side shoots from stubs left when earlier cuttings were taken.

Costa and Costa (1996) promoted side shoots in 15 months old ‘Solo’and ‘Formosa’with the application of cytokinin and gibberellic acid (pH < 2.8) by brushing across the stem, removing flowers, fruits and apical part at the time of treatment application. Desouky et al. (2000) reported that the highest mean number of lateral shoots per plant (18.16 and 15.00, respectively) was obtained with GA (500 ppm), whereas the greatest mean shoot length (5.40 and 5.85 cm) was obtained with GA (1000 ppm) in decapitated eight months old ‘Solo’ seedlings of papaya. Money Junior (2000) recorded higher number of axillary shoots with higher values of diameter and shoot length by treating with BA + GA3 (250 and 500 mg L -1) and reported that in general the decapitation stimulated sprouting in papaya plants. According to Costa and Costa Lateral shoot induction in papaya with plant (2003), plants subjected to application of BAP (500 -1 -1 growth regulators: The production of graftable size mgL ) + GA3 (100 mgL ) resulted in highest scion materials (shoots) from the selected genotypes number of buds on 14-15 cm long shoots, 35 days in papaya is a limiting factor due to apical after treatment and diameter ranging from 1.0 to dominance. Hence, many attempts were made to 2.5 cm. Ono et al. (2004) stated that the removal of overcome this problem in papaya. The method of apical bud did not induce increased formation of buds, painting a lanolin paste mixture of BA (500 mgL -1) but promoted the growth in diameter and length. The -1 and GA (1000 mgL -1) onto the lateral buds of treatment of plants with GA3 (125 mgL ) + BA (125 -1 -1 -1 decapitated stems of 2 year old papaya plant mgL ) and GA3 (250 mgL ) + BA (250 mgL ) stimulated the production of many side shoots from promoted the development and the subsequent apical dominance (Reuveni and Shlesinger, 1990). growth of side shoots. Another efficient option was to spray the stems three Cytokinin is strongly linked with the onset of times at interval of one week with a solution growth of lateral buds and application of cytokinin containing BA (500 mgL -1) and GA (100 mgL -1) stimulates cell division and growth of buds in many which resulted 5-15 cm long and 0.8 to 1.2 cm species. After decapitation, auxin levels in lateral diameter cuttings with 4-5 leaves. Allan and buds increases, levels of ABA decreases and MacMillan (1991) showed that injection of 500 mgL- transport of nutrients and cytokinins from roots 1 BA and 100 mgL-1 GA mixture into the base of the increases lateral bud production (Taiz and Zeiger, stem of 2 m tall plants followed by topping the stem 2004). Giampan et al. (2005) reported the and removing all leaves and fruits a day later, in application of BAP (500 mgL -1) and GA (500 spring, induced the production of large number of mgL -1) on twelve months old ‘Sunrise Solo’trees by

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means of spraying, injection and lanolin paste promoted highest proliferation of lateral shoots, at 30, 55 and 86 days after decapitation. Yang (2009) stated the combination of BA (200 ppm) + GA3 (200 ppm) stimulated the growth of lateral shoots in pot culture experiment whereas, in field experiment on fully developed plants BA (200 ppm) + GA3 (100 ppm) resulted in higher bud sprouting at an average of 3.7 scions per node in 45 days. Anatomy of graft union in papaya: Propagation of plants by asexual means has been practiced for centuries. Recently, it has generated interest among the tree growers. The basis of unity (in grafting and budding) between two parts of plants depends on mutual responsibility. However, successful union of any scion and stock depend upon proliferation of callus tissue between graft components followed by union of vascular tissues. Crafts (1934) found that sieve tubes and xylem elements of Nicotiana glauca and Nicotiana tabacum differentiate as strands in callus a few days after grafting connecting the younger vascular tissue of stock and scion prior to the differentiation of vascular cambium. The orientation of the cambium initials may be determined by these vascular strands. Tewari and Rajpai (1972) and Chakraborthy and Sadhu (1988) found that callus formation and subsequent establishment of cambial contact and vascular continuity between scion and stock were rapid in splice method of grafting in mango. In transverse sections of successful side and veneer graft unions in mango, parenchymatous cells proliferated from both the stock and the scion. It was further observed that the thin walled cells of xylem ray in most recently formed xylem, cambial layers and most recently formed phloem rays were involved in the production of callus tissue (Hoque and Hussain, 1974). Jones (1984) stated the graft tissue influences vegetative shoot growth in apple and cherry by restricting water flow from the root to the shoot or by removing substances, particularly minerals and plant growth regulators (i.e. cytokinins), from the transpiration stream is entirely consistent with the anatomical changes associated with graft tissues. Janick (1986) reported the intermingling and interlocking of callus tissue promotes graft union, differentiates new cambium tissue, which redifferentiates xylem and phloem to form a living, growing connection between stock and scion.

According to Tiedemann (1989), the production of new xylem and phloem permits the vascular connection between the scion and rootstock, where the formation of functional vascular connections is considered as the basic requirement for successful grafts in herbaceous plants. The major hydraulic connection within the graft union of tomato became functional over about 48 hours from the fifth day after grafting, consistent with the appearance of wound xylem bridges (Turquois and Malone, 1996). Based on the MRI images, Leszczynski et al. (2000) reported the cells of cambium divide intensively, produces new cells of turgid and thinwalled secondary phloem and secondary xylem in coniferous plants. Seferoglu et al. (2004) reported that development of cambial continuity and new vascular system formed healthy and successfully at the cross and longitudinal sections of 12 months grafted samples of cherry. The origin of callus tissue from xylem ray cells of both scion and rootstock occur at opposite positions of the vessels of both the scion and rootstock in graft union region of top-cleft grafted jack (Abd El Zaher, 2008). Performance of papaya grafts under field condition: Grafted plants of papaya start to flower soon after planting, at a low height. In Brazil they were found to produce better than seedlings did. Brazilian researchers have experimented with micro-grafting very small seedlings and successfully side grafted plants in the field under tropical conditions (Allan, 2009). Lange (1969) found that grafting papaya on normal dwarfs resulted in plants flowering and producing fruit in the lower stem and with lower productivity compared to papaya ‘Solo’normal. Conversely, grafts of ‘Solo’ dwarf on ‘Solo’normal, resulted in vigorous plants that flowered first in a higher position on the stem with significant productivity and more uniform distribution of fruits along the stem. Ramkhelawan and Baksh (1998) reported at first flowering, the difference in height between seedling plants and those that were terminal wedge grafted, side grafted and chip budded papaya plants were 64.0, 60.9 and 57.9 cm respectively. On the other hand, terminal wedge grafted plants had sturdy appearance and were shorter with much larger stem diameters at the base. FitchMaureen et al. (2005) stated that the clonally propagated papaya plants were significantly shorter

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than seedlings and flowered earlier lower on the trunk at all locations. Stem diameter differences were not significant even though plant size was different at planting time. They were more vigorous and earlier bearing than the seedling plants. In Brazil, Lima de et al. (2010) studied the behavior of three papaya genotypes viz cv. Golden, Sunrise Solo and Hybrid Tainung 01 propagated by grafting. Grafted trees were shorter in height, larger in trunk diameter and bigger in number of leaves and fruits, especially in grafted ‘Tainung 01’. Grafted ‘Solo’ type papaya (‘Golden’and ‘Sunrise Solo’) started flowering forty days after transplanting compared to ninety days for ungrafted one. Grafted papaya trees did not show incompatibility between scion and rootstock and seemed to yield better than ungrafted trees. Pecanha et al. (2010) studied the gas-exchange and photochemical efficiency in seedling and grafted papaya trees grown under field condition. Grafted

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papaya did not show significant differences on gasexchange in all genotypes when compared with seedlings. Chlorophyll fluorescence at 09h00 was the highest (0.83) in Tainung 01 seedlings and the lowest (0.73) in Golden/Tainung 01 combination. CONCLUSION The application of asexual propagation in papaya by grafting would be of great help to the papaya industry. Attempts have been made in this direction in other papaya growing countries like South Africa (Allan, 2007), Brazil (Lima de et al., 2010) and USA (Lange, 1969). Through vegetative propagation, there is a possibility of maintaining the original characteristics of the parent plants apart from advantages like higher yield, lower fruiting height and longer cropping span. Therefore, it has become imperative to standardize a suitable grafting technique for papaya propagation under South Indian situation.

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