Assessment of Morphological, Nutritional and Cytological Characteristics of Some Nigerian Cucurbita Species
Assessment of Morphological, Nutritional and Cytological Characteristics of Some Nigerian Cucurbita Species.
ABSTRACT
Two field experiments were conducted in 2007 and 2008 cropping seasons at the Department of Crop Science research farm, University of Nigeria, Nsukka, to characterize some Nigeria cucurbita genotypes with respect to morphology, nutrient composition and the cytology.
The results obtained showed that Shannon diversity index (Hs) was 4.136 which suggests high level of diversity among the Nigerian cucurbita species evaluated.
Cucurbita moschata had the highest Shannon diversity index of 1.559 followed by C. maxima (1.474) and C. pepo (1.103) thereby revealing C. moschata as the most diverse. The mature fruit colour, seed colour, immature fruit colour, leafiness, petiole colour recorded high Hs values vis-a-vis the other qualitative descriptors.
This is an indication that the above traits contributed meaningfully to the observed diversity in the species. The evenness of C. pepo, C. Maxima and C. moschata were 0.187, 0.250 and 0.265, respectively, suggesting uneven species distribution in the Nigerian agro-ecologies. The genotypes differed significantly (P<0.05) in all the agronomic and yield traits measured.
The only exception was in weight of healthy fruits. The planting season had significant effects (p<0.05) on all the floral and agronomic traits measured with the exception of number of leaves per plant, girth size, vine length, weight of healthy fruits and 100-seed weight.
The interaction of genotype and planting season also had significant effects on days to 50% emergence, number of healthy fruits, number of damaged fruits, 100-seed weight and seed length.
The principal component analysis of the agronomic and yield traits showed that the first three components accounted for 72.20% and 74.75% of the total variation in the 2007 and 2008 plantings, respectively.
The traits representing the genotypes along the first principal axis were 100-seed weight and weight of healthy fruits for the 2007 planting and, number of damaged fruits, seed length and 100-seed weight in the 2008 planting.
Genotypes were differentiated on the basis of days to 50% flowering, fruit diameter, girth size, number of damaged fruits, number of healthy fruits and vine length in the 2007 planting and, days to 50% emergence, number of fruits per plant, number of healthy fruits, number of leaves and weight of healthy fruits in the 2008 planting along the second principal axis.
The hierarchical cluster analysis and cluster plot revealed that the 10 cucurbita genotypes were grouped into two clusters with Akwa-01 alienated from the clusters in the 2007 and 2008 planting seasons.
The coefficients of similarity between the clusters were 0.86 and 0.89 for the 2007 and 2008 plantings, respectively.
The members of cluster I genotypes at both planting seasons are very promising in the production of male and female flowers, ability to sustain larger and healthier fruits. However, genotypes in cluster II are prolific in terms of leaf production and are suceptible to fruit damage.
The correlation coefficient for weight of healthy fruits was highly significant and positive with number of seeds per fruit (r = 0.339**) and days to 50% flowering (r = 0.494**) indicating that increase in these traits will ultimately increase weight of healthy fruits.
The number of male flowers had significant positive relationships with seed length, number of seeds per fruit, fruit length, fruit diameter, number of fruits per plant and number of female flowers indicating that the above traits are influenced linearlly by the number of male flowers.
However, days to 50% emergence was negatively correlated with seed length (r = -0.560**), fruit length (r = – 0.557**), fruit diameter (r = -0.371**), number of fruits per plant (r = -0.430**), number of female flowers (r = -0.543**) and number of male flowers (r = -0.457**).
The chemical composition and nutritional profile differed significantly (p<0.05) among the genotypes in the proximate, mineral, phytochemical and the anti-nutrient analyses.
The results revealed that Pumpkin fruits are very rich in crude protein, minerals (calcium, phosphorus, sodium and iron), phytonutrients (lycopene, ascorbic acid and β-carotene) and crude fibre but low in crude fat, phytate, tannin and moisture content.
The result of the cytological work established a diploid chromosome number of 2n=40 for Cucurbita species at the metaphase stage.
TABLE OF CONTENTS
Title page …….. i
Certification … ii
Dedication ……. iii
Acknowledgement … iv
Co-Authored Articles From This Work ….. vi
Table of contents …….vii
List of Tables ……. viii
List of Figures ……… ix
List of Plates ……. x
Abstract …… xi
Introduction …… 1
Literature Review …. 4
Materials and Methods … 13
Results …… 21
Discussion …. 58
Conclusion …… 68
References ……. 69
INTRODUCTION
Cucurbita belongs to the family, cucurbitaceae which consist of about 118 genera and 825 species (Jeffrey, 1990). The member are warm season annuals, thriving in hot and humid weather (Omafra, 2000) and have spreading growth pattern with tendrils at the leaf axils.
They are important fruit vegetables that are widely grown in the tropics. Leaves are borne singly and may be simple or lobed. Pumpkin is relatively deep rooted and can tolerate dry condition fairly well.
However, extended dry period will result in poor fruit set or poor fruit development and size (Omafra, 2000). It can also tolerate wet condition fairly well but it can induce or increase foliar diseases and fruit rots. The flowers vary considerably in colour and shape and are pollinated by various wild bees (Hurd et al., 1988).
The pumpkin flowers are borne on the axils of the leaves, the males on long peduncles and the females on short peduncles. The female flower contains an inferior ovary (Pumpkin, 2007).
Cucurbita is considered as one of the most morphologically variable genera in the entire plant kingdom (Robinson et al., 1976). Nee (1990) reported that Cucurbita is one of the first plants to be domesticated and that the species are collectively referred to as pumpkin.
Pumpkin is a very important traditional food crop and a great deal of genetic variability has been reported (Montes-Hernandez and Equiarte, 2002). Lust (1983) and Chopra et al. (1986) reported that pumpkin has high nutritional value. Virtually all parts of the plant can be used for food.
Hedrick (1972) stated that pumpkin fruit is a high valued edible fruit; and the fruits can be consumed mature and immature, (Whitaker and Bohn, 1950 and Merrick, 1995). It is consumed either by boiling (leaves and fruits) or by roasting or baking (seeds) (Facciola, 1990).
Pumpkin is rich in nutrient, the seeds can be dried and ground into powder and used with cereals in making bread and cakes while, the seeds are diuretic, tonic and vermifuge. (Chopra et al., 1986).
Pumpkin leaves, fruits, flowers and seeds are all protective and health- giving food. They are rich in vitamin A. and in dietary fiber.
The sub-saharan Africa is not implicated as a centre of origin for Cucurbits. Therefore, the available cultivars are reported to have been introduced by transoceanic traders (Whitaker, 1949). Extensive research works have been carried out on this crop by great researchers in America and Europe.
Carlos (1998) reported that cultivated Cucurbits have many things in common; they are extremely diverse in fruit characters. Some are large fruited, others are small fruited, and every gradation between these extremes does exist.
The principal justification for plant collection is to obtain natural variability that can be useful in producing germplasm pools for crop improvement.
The Cucurbits have diverged from the original descendants of their common progenitor (Benneth, 1970). The Shannon- Weiner Diversity Index is one of the most widely used species diversity indices for examining overall community characteristics.
It was derived from a function, used in the field of information and has been adapted by ecologists to describe the average degree of uncertainty of predicting the species of an individual picked at random from the community.
The uncertainty of occurrence increases both as the number of species increases and as the individuals are distributed more and more evenly among, the species already present.
Kempon and Wedderburn (1978) suggest that this Shannon’s index rely heavily on the abundance of the most common species which may fluctuate widely on year to year basis, and suggests the use of a third diversity index.
The different descriptions of the Cucurbits by different authors have given the classification of the Cucurbita species a controversial status. Many European authors have identified three primary groups namely; Cucurbita pepo group, which includes, C pepo, C moschata, C maxima and C argyrosperma species.
The Cucurbita veruscosa group comprises all the warty varieties of Cucurbits and C. melo group is the scalloped squash (Paris et al., 2002). Linnaeus listed four species of Cucurbita, all of which were classified as C. pepo species by Duchesue (1968). This is because they were related and cross compatible.
Duchesue (1968) isolated two distinct species namely; C. maxima named after the large fruit size and C. moschata for the musky flavour.
Duchesue classified C. pepo as C. poplymorpha in recognition of its extreme variability within the species (Paris, 2001). The CWF (2007) shared the views of the European authors on the description of the warty varieties but classified them as C. veruscosa.
Earlier work (Decker, 1988) suggested that there was a relationship between C. pepo and C. texana and that many edible forms are included in the pepo complex.
Crossibility studies reported by Margaret (2007) revealed that crosses between species are hard to make and their progenies are highly sterile, thus crosses by natural introgression are very unlikely.
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