Breeding of Fruit and Plantation Crops 2 + 1

Methods of Breeding

Introduction:

• The earliest exotic introductions were made in 1924 from Philippines, Malaysia, Fiji, Indonesia, Sri Lanka and Vietnam which formed the nucleus population for many research programmes. The germplasm exchange programme was further intensified in 1952 and in 1958; survey for collection of indigenous germplasm was started. Central Plantation Crops Research Institute (CPCRI), Kasaragod has been designated as the "National Active Germplasm Site" for coconut and maintains the world's largest assemblage of coconut germplasm with 132 acces¬sions which include 86 exotic and 46 indigenous cultivars.

• The World Coconut Germplasm Centre is located at Sipighat in Andaman and Nicobar Islands. Germplasm collections are also maintained at Regional Research Sta¬tion, Kerala Agricultural University, Pilicode and at 11 Coordinating centres, in different States under the AICRP on Palms, These collections are being evaluated for the economic characters such as number of nuts/palm/year, number of bunches, average number of female flowers production, setting percentage, weight of copra/nut, oil content (%) in copra and resistance to pests and diseases in comparison with local cultivars.

Selection:

• Selection aims at retention of desired genotypes and elimination of undesirable ones in the population. This is an important method practised for improvement of coconut. Selection is based on certain visible characteris¬tics of palms that are associated with yield potential such as:

Growth:

• Stout, straight trunks are associated with short, strong bunch stalks and full crown having umbrella/ Spherical shape. Closely spaced leaf scars are a clear indication of a large number of short, strong and well-oriented leaves. A high-yielding palm has more than 30 fully opened fronds.

Nature and Disposition of Crown:

• Short fronds provide adequate support to developing nuts, whereas long fronds fail to support the bunches whereby bunch stalk buckles and causes premature nut fall. The fronds are better oriented in palms with spherical or semi-spherical crown than in those with drooping or erect crown.Nature of Bunch Stalks: Short and stout bunch stalks are better supporters of nuts in bunch and do not require artificial propping. Palms with short fronds and petioles have short bunch stalks also.Number of Inflorescences in the Crown: The number of inflorescences produced largely depends on the number of leaves produced. Regular and heavy bearers usually possess 4-5 leaves more than the medium and poor yielders, with corresponding number of spadices which range from 12 to 15.

Age of Palm:

• In general, palms of 25-60 years old (Middle aged) are recommended because this corresponds to steady period of yield.

High and Consistent Yield of Nuts:

• The number of nuts/ palm is highly variable mainly due to the number of female flowers and percentage of set. Most of the palms are regular-bearers even though a few palms show pronounced alternate bearing habit. Selection should be based on large number of spikelets with only one or two female flowers /spikelet and high-setting percentage. In India, 80 nuts/palm/year is taken as standard.High Copra Output: Copra yield is influenced by the number of nuts produced per year and the weight of copra/nut. High degree of correlation exist between weight of husked nuts and that of copra and high heritability values are observed. Palms producing medium-sized nuts with round or oblong shape weighing not less than 600 g of husked nut and mean copra content of 150 g/nut or more are selected.

High-yielders of Outstanding Breeding Value:

• All high-yielding mother palms need not necessarily produce high-, yielding progenies. Mother palms which produce best prog¬enies have high breeding values. The superiority of progeny can be judged from certain characters at the nursery stage itself. Progeny of high-setting mother palms shows early germination, high collar girth, faster rate of leaf production and early flowering.It is desirable to restrict selection to the best 10% of the palms in each field.

Exploitation of Hybrid Vigour:

• Discovery of hybrid, vigour by Patel (1937) in crosses between West Coast Tall (WCT) and Chowghat Green Dwarf (CGD) is a significant landmark in the history of coconut improvement. This important finding paved the way for successful breeding programmes for high yield in many coconut-growing countries.Intervarietal hybrids with different parental combina¬tions such as Tall x Dwarf, Dwarf x Tall and Tall x Tall were produced in India and Sri Lanka. These hybrids are gaining popularity because of early-bearing and high productivity.

Hybridization:

• Hybridization technique involves emascu¬lation of male flowers before female flowers become recep¬tive, collection of mature flowers from pollen parent, extracting pollen, mixing pollen with diluents in a 1:9 ratio and dusting this mixture using a pollen dispenser. The F1 hybrid production requires controlled pollination using bags for pollination.

• Two methods for commercial production of hybrids are adopted. They are assisted pollination and mass-controlled pollination. Assisted pollination is done in inter-planted seed garden in which lines of seed parents, usually dwarfs, are alternated with a smaller number of pollen parent rows of talls. This method is limited to one hybrid combination. In mass-controlled pollination pollen is sup¬plied to a seed garden that is totally isolated. Different hybrid combinations can then be produced. In both cases, seed gardens are surrounded by 200-300 m wide/barriers of non-coconut vegetation. Individual palms are inspected daily, inflorescence ready-to-open are emasculated and respective flowers are pollinated.

Tall x Dwarf Hybrids:

• Tall varieties are taken as female parent and dwarf varieties as male parent. Among dwarfs, Chowghat Dwarf Orange and Ganga Bondam are best for production of hybrids with West Coast Tall. These hybrids are characterized by early-bearing in 4-5 years, increased yield of nuts with a mean of 100/palm, good quality copra having high content of 176 g and oil recovery of 70%.
  

• The hybrid palms are easily susceptible to soil moisture fluctuations resulting in shedding of buttons and drooping of leaves during summer. When Laccadive Ordinary was used as female parent, the hybrids showed drought tolerance and better yield. The T x D production is time-consuming and laborious when compared to D x T hybrids, since it requires trained climbers for emasculation and hand-pollination of tall-palms.

Dwarf x Tall Hybrids:

• Dwarf varieties are taken as female parent and tall varieties as male parent. The distinct advantage of this hybrid over T x D is that it could be produced on a large scale by regularly emasculating dwarf mother palms, permitting free natural crossing with pollen from tall palms standing nearby. Use of Dwarf Orange or Yellow as female parent enables the identification of hy¬brid seedlings because of colour marker.
  

• Yellow, orange or red petiole colour is recessive to brown and green pigments and hybrids show a greenish-brown or brownish petiole depending on the colour of talls used in crossing. Occurrence of natural cross hybrids (NCD) of dwarfs in the open-pollinated progeny of dwarf is a well-known phenomenon. NCDs are present to the extent of 20%. Hybrid seedlings are selected based on increased vigour and petiole colour.

• D x T hybrids are more vigorous than either of the parents and are prolific yielders. They come to bearing in 4-5 years and out yielded the tall. Field evaluation of coconut hybrids indicated that among T x D and D x T hybrids, D x T was definitely superior to T x D. It was also noticed that tree-to-tree variation was minimum in the hybrid. The nut and copra characters are superior to dwarfs and more or less similar to talls. The hybrids occasionally show a tendency for alternate-bearing, bunch, buckling, and susceptibility to moisture fluctuations, resulting in button shedding and drooping of leaves.

• Use of Malayan Yellow Dwarf as female parent gives 95-97% recovery of hybrids, since it is more homozygous due to self-pollination. In combinations involving Chowghat Dwarf Orange, hybrid recovery is only 30% since it is not completely homozygous. For production of stable hybrids with high economic value, selection of cultivars with wide genetic make-up, selection of hybrid combiners and use of inbred talls as male are recommended.

Tall x Tall Hybrid:

• The T x T hybrids are produced by intravarietal hybridization of tall cultivars under control¬led conditions. Individual palms of high-breeding value are identified and utilized for production of T x T hybrids. Though late in bearing, the yield potential of T x T hybrids are good.

Breeding for Special Characteristics

Drought Tolerance:

• A low average rainfall (< 150 mm/ month) and erratic distribution adversely affect the yield of palm. The traits identified for predicting drought tolerance in coconut are accumulation of epicuticular wax on leaf surface, low stomatal frequency, low stomatal resistance and leaf water potential. Based on these char¬acters, the drought tolerant cultivars identified are Feder¬ated Malay States, Java Giant, Fiji, Laccadive Ordinary and Andaman Giant. Laccadive Ordinary was more toler¬ant to drought and hybrids LO x COD and LO x Ganga Bondam also, show tolerance to drought.

Disease Resistance:

• Screening of the germplasm collec¬tions and hybrid combinations against root wilt, the most devastating disease in coconut, was not successful. 'Hot spot' areas of root wilt were surveyed and palms were identified.Chowghat Green Dwarf (CGD) palms, which are disease-free, are being utilized in breeding programmes. Breeding for resistance to coconut root wilt disease resulted in the development and release of two resistant varieties viz. Kalparaksha (MGD selection) and Kalpasree (CGD selection) and one tolerant hybrid viz. Kalpasankara (CGD x WCT) for cultivation in the root wilt prevalent areas.

Germplasm Exchange:

• Prevalence of root wilt disease in Kerala, Tatipaka disease in Andhra Pradesh, Tanjavur and Ganoderma wilts in Tamil Nadu restrict the movement of germplasm especially with other countries. However, coconut germplasm from India can be obtained with the approval or ICAR, New Delhi. The nodal agency for coordinating germplasm exchange in India is NBPGR, New Delhi, while CPCRI, Kasaragod, is the agency for phytosanitary clearance. At the international level, Inter-national Coconut Genetic Resources Net Work (COGENT) under IPGRI is responsible for the introduction and ex¬change of coconut germplasm with the financial support from FAO and ADB. The COGENT restricts the movement of coconut germplasm through seeds and permits zygotic embryos.