Self Incompatibility

Dhamayanthi et al. (2003) investigated the self-incompatibility system in ginger. They reported that heterostyly with a gametophytically controlled self-incompatibility system exists in ginger. Flowers are distylous, there are long ("pin") and short ("thrum") styles. The "pin" type has a slender style that protrudes out of the floral parts, which are short, covering not even half the length of the style. The stigma is receptive before the anthesis, whereas the anthers dehisce after 15 to 20 hours. The anthers are situated far below and hence the pollen grains cannot reach the stigma. In case of the "thrum" style, the stigma is very short and the staminodes are long and facing inward. However, the occurrence of thrum styles is very rare among cultivated ginger. According to the above-mentioned workers, this heterostyly situation may be a contributing factor to the sterility in ginger. However, this may not be very important as almost all cultivars are the pin type and pollination is entomophilous, mostly by honeybees. Dhamayanthi et al. (2003) have also reported inhibition of pollen tube growth in the style, and this was interpreted to be due to incompatibility. Adaniya (2001) reported the pollen germination in a tetraploid clone of ginger, 4 X Sanshu. Pollen germination was highest at around 20°C and pollen tube growth in the style was greatly enhanced at 17°C. At this temperature, the pollen tubes penetrated into the entire length of the style in

66.7% of the styles analyzed. Pollen stored for 3 hours at a relative humidity (RH) of 40 to 80% completely lost its viability, whereas pollen incubated at 100% RH retained relatively high germinability. When the RH was low, the pollen tube in the style stopped growing. Hence for pollen to germinate and grow in the stylar tissue, relatively low temperature (approximately 20°C) and 100% RH are essential.

Embryology

The embryology of ginger has not been investigated critically so far, and it is rather amazing that such an economically important species has been ignored by embryologists. One possible reason may be the absence of flowering and seed set in ginger in most growing regions. However, some information is available on a related species, Z. mac-rostachyum. The embryological features of the genera in Zingiberaceae are similar, and hence the information on Z. macrostachyum may as well be applicable to ginger.

The embryo sac development follows the Polygonum type (Panchaksharappa, 1966). The ovules are anatropous, bitegmic, and crassinucellate and are borne on an axil placentation. The inner integument forms the micropyle. In the ovular primordium the hypodermal archesporial cell cuts off a primary parietal cell and a primary sporogenous cell (Figure 2.10). The former undergoes anticlinal division. The sporogenous cell enlarges into a megspore mother cell, which undergoes meiosis forming megaspores. The chalazal spore enlarges and produces the embryo sac. Its nucleus undergoes three successive divisions resulting in a eight-nucleate embryo sac. Prior to fertilization in Z. macrostachyum, the synergids and antipodals degenerate. The fate of the nuclei in the embryo sac of ginger (which is a sterile species) is not known. However, some studies have indicated a postmeiotic degeneration of the embryo sac (Pillai, personal communication).

Cytology, Cytogenetics, and Palynology Mitotic Studies

The chromosome number of ginger was reported as 2n = 22 by Moringa et al. (1929) and Sugiura (1936). Darlington and Janaki Ammal (1945) cited a report from Takahashi who claimed 2n = 24 for Z. officinale. A more detailed study was carried out by Raghavan and Venkatasubban (1943) on the cytology of three species, Z. officinale, Z. cassumunnar, and Z. zerumbet, and all three had the somatic chromosome number of 2n = 22. Based on the differences in ideogram morphology, the above-mentioned workers concluded that the chromosome morphology of Z. officinale was different from the other two species. Janaki Ammal (Darlington and Janaki Ammal, 1945) reported two "B" chromosomes in certain types of ginger in addition to the normal complement of 2n = 22. Chakravorti (1948) also found 2n = 22 in ginger. He concluded that in view of the normal pairing of 11 bivalents in species like Z. cassumunnar and Z. zerumbet, Z. mioga having a somatic chromosome of 2n = 55 is to be considered a pentaploid (Table 2.3).

Sharma and Bhattacharya (1959) reported the widespread occurrence of an inconsistency in chromosome numbers in several species of Zingiberaceae including Z. officinale. Sato (1960) carried out karyotype studies of 24 species belonging to 13 genera and concluded that the basic number of the genus Zingiber is x = 11 and that Z. mioga

Figure 2.10 Embryology of ginger (Z. macrostachyum). 1—8, stages in the development of the embryo sac (for details see text).

1. L.S. of the anatropous ovule. 2. L.S. ovule showing archesporial cell. 3. L.S. ovule with meagspore mother cell. 4. T-shaped tetrad. 5, 6. 4- and 8-nucleate embryo sacs. 7, 8. Organized embryo sacs. Note the degenerated synergids and antipodals in 8.

Figure 2.10 Embryology of ginger (Z. macrostachyum). 1—8, stages in the development of the embryo sac (for details see text).

1. L.S. of the anatropous ovule. 2. L.S. ovule showing archesporial cell. 3. L.S. ovule with meagspore mother cell. 4. T-shaped tetrad. 5, 6. 4- and 8-nucleate embryo sacs. 7, 8. Organized embryo sacs. Note the degenerated synergids and antipodals in 8.

having 2n = 55 is a pentaploid. Ramachandran (1969) studied the cytology of five species of Zingiber (Z. macrostachyum, Z. roseum, Z. wightianum, Z. zerumbet, and Z. officinale) and found a diploid number of 2n = 22 in all species. He found evidence of structural hybridity involving interchanges and inversions in ginger. Mahanty (1970) studied the cytology of Zingiberales. He reported 2n = 22 for Z. spectabile and Z. cylindricum and concluded that the genus Zingiber appears to be much more correctly placed in Hydychieae than in the Zingibereae.

Ratnambal (1979) investigated the karyotype of 32 cultivars of ginger (Z. officinale) and found that all of them possess a somatic chromosome number of 2n = 22 (Figure 2.11). The karyotype was categorized based on Stebbins's classification (Stebbins, 1958), which recognizes three degrees of differences between the longest and the shortest chromosome of the complement and four degrees of differences with respect to the

Table 2.3 Chromosome reports on Zingiber

Species

n

2n

Reference

Z. officinale

Was this article helpful?

0 0
Aromatheray For Cynics

Aromatheray For Cynics

This eBook explains how Aromatherapy has something to do with scents and smells treating illnesses and conditions. Many people who do not like the sometimes-unpleasant side effects of prescribed medication, particularly for depression, stress, or other similar disorders, have opted to use aromatherapy to help reach the desired state of being.

Get My Free Ebook


Post a comment