Statistical analysis of variability ia a population of Xiphinema basiri Siddiqi, 1959

Abstract

The characters used in nematode taxonomy vary among and within populations of a single species. The variations may be host-determined or due to differences in the environment (ecophenotypic variations) or due to different geographical distribution of the populations. These have been studied by various authors. J. B. Goodey (1952) demonstrated host-induced variations in body length and dorsal or ventral positions of the oesophageal bulb in Ditylenchus destructor. Rhode and Jenkins (1957) found that body length and body width of Trichodorus christiei vary inversely with the temperature of soil. Taylor and Jenkins (1957) working with Pratylenchus spp. and Coomans (1962) with Rotylenchus goodeyi found that deviations from the mean were least for vulva position and greatest for tail shape. Sturhan (1963) found that body width, oesophageal and tail lengths of Xiphinema and Longidorus species exhibit negative allometric growth with body length. Tarjan (1964) noticed differences between north-western and south-eastern populations of X. bakeri in body length, values of a and b, posterior gonad length, and in c' ratio. Gysels (1964) observed that temperature influences allometric growth of Panagrellus silusiae. Fisher (1965) demonstrated variations due to host plant and temperature in the body and stylet lengths of Pratylenchus nanus. The host species and variety, host physiology and the geographical origin of a population was found to influence the variations in morphometric and allometric characters in T. christiei and the stylet length and the value of V were least variable characters (Bird and Mai, 1967). Baqri and Jairajpuri (1967) studied the variations within 14 populations of Thornenema mauritianum from India. The variations among different populations of X. americanum from different parts of the world were possibly due to geographical latitude, temperature and other factors (Tarjan, 1969). Loof and Maas (1972) observed intraspecific variations among the populations of Xiphinema species found in Surinam and concluded that body dimensions alone are unsatisfactory for distinguishing species and qualitative characters should also be given at least equal weight. Heyns (1974a and 1974b) studied intraspecific variations in X. brevicolle and X. elongatum which may be correlated with the geographical distribution of the various populations. Bajaj and Jairajpuri (1977) studied variability within 23 populations of X. insigne from India and grouped them in two ({ forms », viz., indicum-form and insigneform. Morphometric and allometric variations in a population of Helicotylenchus indicus have been studied by Azmi and Jairajpuri (1977). Xiphinema basiri Siddiqi, 1959 is fairly well distributed in India, especially in the plains, and in Aligarh is of common occurrence. Specimens from different populations of X. basiri show variability in length of body, odontostyle and tail and in the shape of lip region and tail. However, not only do the specimens from different localities (geographical variations) and hosts (host-determined variations) show variability but also the specimens from a single population are variable. In this paper an attempt has been made to study the statistical significance of these variations in a single natural population of X. basiri collected from soil around roots of citrus plants from the gardens of Botany Department, Aligarh Muslim University, Aligarh. The variability was studied in the adults as well as in the juveniles. In addition, certain abnormal morphological variations were also noticed in the development of the gonads and in tail shape. These are described below.