Chapter 1: Review of literature
1.6 Germplasm characterization
Characterization of genotypes is fundamental for breeding and strategic conservation. To serve the diverse human needs the genetic diversity of ‘underutilized’ and ‘neglected’ crops like bottle gourd needs to be harnessed through an effective pre-breeding program. The standard descriptors for bottle gourd have been used as guidelines in phenotypic characterization (Morimoto et al., 2005;
Yetişir et al., 2008). Table 1.1 summarizes some qualitative traits that have been used for bottle gourd phenotyping. The diversity represented especially by fruit qualitative provides an important basis for the breeding of new bottle gourd cultivars. Qualitative traits form discrete phenotypic classes that can be assessed visually and are therefore useful for breeding and genetic analysis of the crop (Manivannan et al., 2016). Several genes controlling different qualitative traits have been described in bottle gourd (Table 1.2). Inheritance studies of several qualitative traits are yet to be studied in bottle gourd including blossom and stem-end fruit shape, presence or absence of fruit neck, fruit neck length and other fruit shapes (e.g. necked vs non-necked, pyriform vs elongated and snake-like vs. curvilinear etc.).
Table 1.1. Summary of qualitative traits used in genetic diversity analysis in bottle gourd.
Trait Class Reference
Seed size Small Yetisir et al. (2008)
Medium Large
Seed margin Absent Yetisir et al. (2008)
Thin and uniform Thin and irregular Thick uniform Thick irregular
Seed margin color Absent Yetisir et al. (2008) White
Tan Yellow Orange Brown Grey Black Light brown Dark brown
Cotyledon size Small Yetisir et al. (2008)
Intermediate Large
Cotyledon color Light green Yetisir et al. (2008) Intermediate
Dark green
Leaf shape Ovate Yetisir et al. (2008)
Orbicular Reniform Retuse Heart
Leaf size Small Yetisir et al. (2008)
Intermediate Large
Leaf edge Smooth Yetisir et al. (2008)
Toothed
Leaf pubescence Small Yetisir et al. (2008)
Intermediate Large
Pubescence of upper Small Yetisir et al. (2008) surface of leaf Intermediate
Large
Branching pattern Central Mashilo et al. (2015) Basal
Table 1.1. (Continued)
Trait Class Reference
Peduncle transactional Round Yetisir et al. (2008)
Shape Slightly angled
Angled
Peduncle attachment Easy Yetisir et al. (2008) Intermediate
Difficult Stem end fruit shape Depressed
Yetisir et al. (2008) and Sivaraj and Pandravada (2005)
Flattened Rounded Pointed Blossom end shape Depressed
Yetisir et al. (2008) and Sivaraj and Pandravada (2005)
Flattened Rounded Pointed
Fruit shape Oblate Sivaraj and Pandravada (2005)
Circular Pyriform
Elongated pyriform Cavate
Cylindrical
Variation in fruit shape Low Yetisir et al. (2008) Intermediate
High
Table 1.2. Genes controlling some qualitative traits in bottle gourd.
Gene Description Reference
Bb Bottle-shaped fruit Tyagi (1976)
BB Disk-shaped fruit Tyagi (1976)
Rr Produces round-shaped fruit Tyagi (1976)
GG Dark green fruit colour Tyagi (1976)
Gg Light green fruit colour Tyagi (1976)
Lblb Light brown seed coat colour Tyagi (1976)
LbLb Brown seed coat colour Tyagi (1976)
WtWt Warty fruit texture Mladenovic et al. (2013)
Wtwt Smooth fruit texture Mladenovic et al. (2013)
Genetic diversity in bottle gourd has also been described based on quantitative phenotypic traits (Morimoto et al., 2005; Yetişir et al., 2008; Koffi et al., 2009; Mladenovic et al., 2012; Xu et al., 2014). Quantitative traits widely reported in genetic diversity studies are summarized in Table 1.3.
Coefficient of variation (CV’s) in these studies tended to be larger for fruit traits than other quantitative traits indicating that bottle gourd is more diversified in fruit size and fruit shape (Morimoto et al., 2005; Sivaraj and Pandravada, 2005).
Table 1.3. Quantitative phenotypic traits and corresponding mean values reported in bottle gourd.
Quantitative trait Mean Reference
Days to 50% female flowering 54.2 (7.38) Harika et al. (2012) Number of nodes on main-stem 5.21 (5.9) Harika et al. (2012)
Sex ratio 17.4 (9.2) Harika et al. (2012)
Number of branches 8.89 (5.1) Harika et al. (2012)
Number of fruits per plant 7.62 (7.5) Harika et al. (2012)
Fruit mass (kg) 1.1 (8.3) Harika et al. (2012)
Fruit length (cm) 35.6 (7.2) Harika et al. (2012)
17.8 (60) Morimoto et al. (2005) 38.7 (51.7) Sivaraj and Pandravad (2005)
Fruit width (cm) 8.77 (17.7) Harika et al. (2012)
10.8 (33) Morimoto et al. (2005) 19.3(38.3) Sivaraj and Pandravad (2005) Fruit circumference (cm) 42.2(39.1) Morimoto et al. (2005)
Volume of fruit (cm3) 1016 (93) Morimoto et al. (2005)
Length between apical point and wide fruit part
(cm) 5.6 (40)
Morimoto et al. (2005) Relative length of fruit width 0.76 (45) Morimoto et al. (2005) Relative length of the apical point 0.36 (32) Morimoto et al. (2005)
Shell thickness (cm) 2.87 (10.6) Harika et al. (2012)
0.42 (39) Morimoto et al. (2005) 0.31 (9.7) Sivaraj and Pandravad (2005) Number of seeds per fruit 304 (50) Morimoto et al. (2005)
Seed length (cm) 1.32 (16) Morimoto et al. (2005)
1.67(10.7) Sivaraj and Pandravad (2005)
Seed width (cm) 0.68 (16) Morimoto et al. (2005)
0.74 (9.6) Sivaraj and Pandravad (2005)
Seed size (cm²) 0.92 (32) Morimoto et al. (2005)
Hundred seed weight (g) 14.05 (8.1) Harika et al. (2012)
17.9 (26.8) Sivaraj and Pandravad (2005)
Days to maturity 63.61 (6.9) Harika et al. (2012)
Values in parenthesis are coefficient of variation (CV) in percentages.
Germplasm characterization using morphological markers is an important first step in the
mainly depends upon the magnitude of morphological variability (Smith et al., 1991; Belaj et al., 2011). Morphological characterization facilitates efficient utilization of germplasm collections in a breeding program, providing direct useful information about the genetic relationships and specific traits of agronomic importance (Laurie et al., 2012). However, assessment of variability based on agro-morphological characteristics has limitations, since most of the characters are influenced by environmental factors and plant developmental stage (Morimoto et al., 2005; Dey et al., 2006; Behera et al., 2012). Therefore, genetic diversity analysis using morphological characterization can be complemented by other tools such as DNA based molecular markers for accuracy or repeatability.