Breeding and Genetics,
University of Agriculture, Faisalabad, Pakistan.
Pea (Pisum sativum L.), family Papilionaceae, is a multipurpose crop. Pea (Pisum
sativum L.) is the second important food legume in the whole world after
Phaseolus vulgaris (Tar’an et al., 2005). The genus Pisum contains two species,
Pisum sativum and Pisum fulvum both with 2n =14 chromosomes. Four centers of
origin based on genetic diversity were listed by Vavilov (1926) central Asia,
the Near East, Abyssinia and the Mediterranean. Blixt (1970) indicated that the
principal center of genetic diversity is the Mediterranean center with secondary
centers in the Near East and Ethiopia .
Pea is an important winter crop of west Europe, North America, India, Australia,
Pakistan and South America. Among the grain legumes, dry peas (Pisum sativum)
rank first regarding production in Europe. Pea is among the four important
cultivated legumes next to soybean, groundnut and beans (Husle, 1994). Powdery
mildew disease causes the crop damages reaching as high as 25% to 86%. It is a
cheap source of protein that is known as poor man meat in the developing world
and used in rotation with cereals and oil seed crops. It provides balanced diet
in combination with wheat, rice and other cereals. The dried peas contain 1.4%
fat, 60.7% car¬bohydrate, 10.9% protein, 1.4% crude fiber and 2.7% ash (Tzitzikas
et al., 2006). Increasing value of protein enriched food has led to a greater
chance in this crop as a protein source (Santalla et al., 2001).
In Pakistan it is cultivated under an extensive range of agriculture regions,
but the average yield per hectare is very low as compared to its potential and
yield obtained in many other countries. It is cultivated during winter in
Pakistan and during summer in highlands (Habib and Zamin, 2003). It represents
about 40% of the total trade in pulses.
Vegetable crops have secondary importance in crop husbandry in Pakistan, so very
little importance is given to their improvement. In Pakistan during 2009, the
crop was grown over an area of 11689 ha with 83603 tones production of green pea
and average yield was 178.8 mounds /ha but the aver¬age per hectare yield is
very low (Anonymous, 2010-11). This may be attributed due to non adoption of
approved varieties, irrigation schedule and recommended agro practices,
deviation from normal planting and optimal seed rate. Non application of
fertilizers, weed infestation, diseases, harvesting losses also play an
important role. Powdery mildew, caused by Erysiphe pisi, is the most extensive
disease of pea in the world.
The correlation studies provide information about association between any two
characters. The path coefficient analysis provides the division of correlation
coefficients into direct and indirect effects giving the relative importance to
the causal factors. The current study was carried out in order to find out the
genetic variation, interrelationships among different characters and the direct
and indirect contributions of these characters towards yield.
The understanding of association of characters is of very importance in
developing an efficient breeding program. The prime and long term objective of
plant breeding is to increase productivity to meet the increasing food demands
of people. New varieties with improved agronomic traits have been the major
contributing factor to increase food production. The estimate of genetic
diversity and its relationship with germplasm collections and evaluation are
useful for facilitating efficient germplasm collection, control and utilization
(Nisar et al., 2008).
The present study aims at the estimation of direct and indirect contribution of
different yield components to the overall seed yield in peas. Availability of
genetic variability is crucial for any breeding programme which provides
opportunity for selection of desirable genotypes. In the process of selection
correlation plays an important role because genetic correlation between the
selected traits and other traits affects the process significantly (Falconer and
Mackay, 1996).
Using the correlation techniques, the response of a correlated character can be
predicted if the genetic correlation and heritability of two characters are
known. It serves as an additional source of information for the plant breeder
(Falconer and Mackay, 1996). The genetic analysis of traits will help in
identifying and screening those genotypes which can be used in the development
of good plants. The result of the study might be helpful for the plant breeder
in a breeding programme for developing good varieties and it will help in
achieving food security.
The present study was conducted for the estimation of correlation and path
analysis for quantitative traits in peas (Pisum sativum L.) in the area of the
department of Plant Breeding and Genetics, University of Agriculture,
Faisalabad, Pakistan during the winter season 2009-2010. The experimental
material comprised thirty genotypes of peas Viz. (6173, 1172, Dasan, Rondo,
Siddique 1, 6121, PF- 450, IT-450, Little Marvelose, 380, Parker, VIP, Winer, Fs
2187, 200160, GRW -45, Green Arrow, 267, Climax, S – Green, Lampo, Meteor – 3,
Liana Pak, 5180, Rohina, Azad P1, PF -400, Little Morvel, Meteor -1 and Sitara
Gold). These genotypes were sown in a randomized complete block design (RCBD)
with three replications under normal conditions. Interrelationships of various
quantitative traits like days to 50 % flowering, number of nodes, plant height,
number of branches per plant, pod length, pod width, pod weight, seed yield per
plant , number of pods per plant, shelling % age, 100-grain weight, number of
seeds per pod and seed yield per plant were ascertained.
Variability estimates revealed that significant genetic variability existed
among the genotypes for the characters under study. The phenotypic coefficients
of variation (PCV) were invariably slightly higher than their corresponding
genetic coefficients variation (GCV) due to the influence of environment on
character expression. Further comparison of the genotypes showed that genotype
PF- 400 had a batter yield performance. Highest heritability estimates for
characters plant height and number of pods per plant while other characters
showed moderate heritability. Heritability for these traits indicated that
selection could be more effective for genetic improvement. Correlation studies
showed that pod weight, number of pods per plant, number of branches per plant,
number of seeds per pod and 100-seed weight were positive and significant
correlation at genotypic level but positive and highly significant correlation
at phenotypic level. Whereas number of days to 50 % flowering, shelling % age,
number of nodes per plant, pod length were positively correlated with the grain
yield per plant at genotypic and phenotypic levels. Plant height and shelling %
age was negative and non-significantly correlated with grain yield per plant at
both genotypic and phenotypic levels.
The path coefficients were also calculated to estimate the contribution of
individual characters to the seed yield. Investigations regarding path
coefficient showed that number of days taken to 50 % flowering and number of
branches had maximum direct effect on grain yield per plant followed by number
of nodes per plant, seeds per pod, 100 seed weight and plant height. The number
of grains per plant, number of pods per plant, number of number of branches per
plant had negative direct effects on grain yield.