MSc

Rambutan ( Nephelium lappaceum L.) or ‘hairy litchi’ is an exotic fruit crop with tremendous potential for cultivation in the whole state of Kerala. There exists great variability in rambutan because of the natural cross pollination and seed propagation, which in turn provides great scope for selection.
It is in this context that the hundred variable types of rambutan collected from important rambutan growing tracts of Kerala (Pathanamthitta-40, Kottayam-37, Thrissur-18 and Idukki-5) were evaluated for various morpho-physiochemical traits in addition to sensorial perception. The study was taken up with the prime objectives of recording the existing variability and genetic wealth available in order to select and conserve the elite/promising types and thereby, to serve as a basis for promotion of cultivation of this exotic fruit crop in Kerala. The study confirmed that rambutan fruits varied widely in their morpho-physical and biochemical traits such as tree characters, inflorescence characters, fruit characters and quality parameters, which were recorded as per IPGRI crop descriptor.
Flowering and fruiting were characters more observed to be a function of the location. The study on phenological growth stages of rambutan according to BBCH scale in different locations opens out a new area on the possibility of staggered fruit production of rambutan in Kerala. The fruits are available from May to October (if cultivated in the humid tropical plains as in Thrissur, Kottayam and Pathanamthitta as well as in the humid sub-tropical belts as in the high ranges of Wayanad), thus making the availability of fresh fruits for nearly half period of a calendar year.
With regard to the individual fruit weight, highest fruit weight of 61.5 g was recorded in Col.052 and the lowest fruit weight of 12 g was observed in Col.012 and Col.013. The largest proportionate edible part was found in Col.072 (52%) and the lowest in Col.008 (15%). Free seed aril was found in 19.39 per cent of the collections, while the adherence of aril to seed was medium in 16.33 per cent of the collections. Only 8.16 per cent of the collections produced fruits which could be characterized as very juicy types and 47.99 per cent were grouped as juicy type. About half of the collections (48.97%) had a TSS above 20° Brix. The collections having TSS above 25° Brix (Col.015 with 26° Brix and Col.061 with 27.5° Brix) were classified under the category ‘very sweet’. The titrable acidity and total sugar content ranged from 0.12 to 1.4% and 13 to 18.4% respectively.
The loading plot based on tree characters revealed significant positive correlations between rachis length and leaflet width; leaflet width and leaflet length and between tree age and number of leaflets per leaf. Strong positive associations were also observed among fruit characters such as fruit weight, fruit diameter, rind weight, aril weight, aril thickness and spine length.
The principal component analysis performed based on tree characters revealed the major contribution of leaflet length, leaflet width and petiole length towards the genetic divergence in rambutan and about 75 per cent of the total variance in fruit characters was mainly determined by the traits such as fruit weight, aril weight, aril thickness, seed weight, seed width, titrable acidity, TSS and sugar content.
Clustering of all the three categories of rambutan collections namely elite, export and industrial use types using score plot confirmed the superiority of six collections (Col.021, Col.022, Col.023, Col.052, Col.55 and Col.061) over others, which were selected further for developing a selection criteria in rambutan. In the sensory analysis, Col.061, Col.021 and Col.042 were most preferred/accepted by panelists because of their better fruit weight, taste, juiciness and easy detachment of aril from seed.
Two new pests of economic importance (fruit borer, Conogethes punctiferalis and fruit webber, Eublemma anguilifera) have been identified from the rambutan growing tracts of Kerala from fruit set to fruit ripening stage. Their nature of damage and symptoms of infestation have been clearly studied and being reported for the first time in rambutan from India.
The study revealed that rambutan selections from Kerala are not only comparable with the best known cultivars in the world, but even excell them. There is an urgent need to standardize the management practices including the varietal wealth in rambutan by using these genetic resources as this crop has already become one of the most treasured fruit particularly as a courtyard crop in Kerala.