Anand P. Tyagi

Correlation and path coefficient analysis in sugarcane

Correlation and path coefficient analysis was undertaken among agronomic and bio-chemical characters of importance in sugarcane. Correlation between agronomic characters revealed positive and significant (P = 0.01) correlation between plant volume and number of millable stalks (0.874), plant volume and weight per stalk (0.812), plant volume and weight of millable stalks (0.962), plant volume and stalk thickness (0.842), number of millable stalks and weight of millable stalks (0.889) and other agronomic characters. There was a non-significant but positive correlation between number of millable stalks refractrometer brix (0.05), number of millable stalks and stalk height (0.285) and other characters. In case of bio-chemical characters, positive and significant (P = 0.01) correlation was recorded between Pure Obtainable Cane Sugar (POCS) and pol (0.901), POCS and purity (0.763) and pol and purity (0.780). Negative but non-significant correlation was observed between POCS and fibre. Correlation studies indicate that for sugarcane yield plant volume, plant height, number of millable stalks per stool, stalk thickness and weight of millable stalks are the most important characters. However, for biochemical characters POCS, pol and purity are the most important characters. Path coefficient analysis in the case of agronomic characters showed revealed that the weight of millable stalks was the most important character with the highest direct effect on sugarcane yield followed by stalk height, number of millable stalks and stalk thickness among agronomic traits. In bio-chemical characters highest direct effect was on percent POCS followed by percent purity and percent fibre. In nutshell correlation and path coefficient analysis in present study suggests that clones or varieties with high plant volume, plant height, and other agronomic characters should be used in hybridization programme.

Large-scale polymorphism of heterochromatic repeats in the DNA of Arabidopsis thaliana

BackgroundThe composition of the individual eukaryotes genome and its variation within a species remain poorly defined. Even for a sequenced genome such as that of the model plant Arabidopsis thaliana accession Col-0, the large arrays of heterochromatic repeats are incompletely sequenced, with gaps of uncertain size persisting in them.ResultsUsing geographically separate populations of A. thaliana, we assayed variation in the heterochromatic repeat arrays using two independent methods and identified significant polymorphism among them, with variation by as much as a factor of two in the centromeric 180 bp repeat, in the 45S rDNA arrays and in the Athila retroelements. In the accession with highest genome size as measured by flow cytometry, Loh-0, we found more than a two-fold increase in 5S RNA gene copies relative to Col-0; results from fluorescence in situ hybridization with 5S probes were consistent with the existence of size polymorphism between Loh-0 and Col-0 at the 5S loci. Comparative genomic hybridization results of Loh-0 and Col-0 did not support contiguous variation in copy number of protein-coding genes on the scale needed to explain their observed genome size difference. We developed a computational data model to test whether the variation we measured in the repeat fractions could account for the different genome sizes determined with flow cytometry, and found that this proposed relationship could account for about 50% of the variance in genome size among the accessions.ConclusionOur analyses are consistent with substantial repeat number polymorphism for 5S and 45S ribosomal genes among accession of A. thaliana. Differences are also suggested for centromeric and pericentromeric repeats. Our analysis also points to the difficulties in measuring the repeated fraction of the genome and suggests that independent validation of genome size should be sought in addition to flow cytometric measurements.

Location and interseasonal variation in flowering, propagule setting and propagule size in mangroves species of the family Rhizophoraceae

Three species of mangroves, Rhizophora stylosa, Rhizophora mangle (synonym R. samoensis) and Bruguiera gymnorhiza in the family Rhizophoraceae were studied to understand the flowering pattern, propagule development and the propagule size at maturity prior to dispersal from the mother plant. The study was conducted in the Wet and the Dry zones over two seasons in Viti Levu, the Main Island of Fiji. The flower number, number of propagules and propagule size at maturity were significantly different among three species and within species in the Dry and the Wet zones. Only 1–2% of total flowers in each species became mature propagules. This percentage was significantly lower in the Dry zone for all three species. Rhizophora stylosa produced the biggest size of propagules followed by Rhizophora mangle and Bruguiera gymnorhiza. Relatively longer and heavier propagules were recorded in the Wet zone and shorter and lighter in the Dry zone. Inter-seasonal differences were not significant for these characters. This could be mainly due to almost similar amount of rainfall, relative humidity and temperature regimes over two seasons within each zone.

Pollen Fertility Status in Coastal Plant Species of Rotuma Island

and Abstract The Island of Rotuma is facing widespread destruction and degradation of its flora. This investigation was conducted to determine the pollen fertility status in thirty two species of economic and environmentally important coastal species, which are reproducing freely thus most suitable to rehabilitate coastal areas. Pollen fertility status in these species varied from as low as 38% in Canavalia cathertica to as high as 100% in Hernandia nymphaeifolia and Vigna marina. It was interesting to note that species within same genus showed wide range of pollen viability. However, most of the species investigated had high pollen viability especially in those species, which grow close to sea. It was recorded that pollen fertility was low in small fragmented populations. This showed the effect of population size on reproduction. Larger sized populations showed high percentage of pollen fertility.

Improving taro (Colocasia esculenta var. esculenta) production using biotechnological approaches.

Taro (Colocasia esculenta L. Schott) is an important crop worldwide but is of particular significance in many Pacific Island countries where it forms part of the staple diet and serves as an export commodity. Escalating pest and disease problems are jeopardizing taro production with serious implications to food security and trade. Biotechnological approaches to addressing pest and disease problems, such as somatic embryogenesis and transgenesis, are potentially viable options. However, despite biotechnological advancements in higher profile agronomic crops, such progress in relation to Colocasia esculenta var. esculenta has been slow. This paper reviews taro biology, highlights the cultural and economic significance of taro in Pacific Island countries and discusses the progress made towards the molecular breeding of this important crop to date.

Comparison of performance of whitewood (Endospermum medullosum L.S. Smith) provenances and families in Vanuatu

This study reports a comparison of performance of four year-old whitewood (Endospermum medullosum L S Smith) provenances and families trials established by the Department of Forestry of Vanuatu and the South Pacific Regional Programme In Forest Genetic Resources project (SPRIG). Trees in the different open-pollinated, half-sibling families had mean heights ranging from 7.1 m to 10.2 m, dbh from 13.5 cm to 17.8 cm, wood volume from 0.07 to 0.14 m3 and survival from 54% to 91%. Seedlot GD11 from Shark Bay East Santo showed the superior mean height of 10.2 m followed by seedlot MT29 from Maewo and MS47 from Malel Central East Santo with 9.6 m. The shortest trees were in families JT35 (Forari, Efate) with 7.1 m, MT33 (Maewo) and JT30 (Forari, Efate) with 7.5 m. Trees in seedlots MS44 from Malel Central East Santo and MS32 from Palon East Santo had the biggest diameter increase(mean dbh of 17.8 cm) followed by seedlot GD11 Shark Bay East Santo and MS2 from Sara East Santo with 17.5 cm and MS55 from South East Santo with 17.4 cm. Seedlots with very low diameter increment were MT3 from Maewo and JT35 from Forari (mean dbh of 13.5 cm) followed by MT3 and MT4 from Central Pentecost with a mean dbh of 13.8 cm. Seedlots with superior wood volume production were MS2 from Sara East Santo (with mean of 0.15 m3 per tree) followed by seedlots MS32 Palon East Santo, GD11 Shark Bay East Santo, MS55 South East Santo with 0.14 m3 and MS3 Kole East Santo with 0.13 m3. The slowest growing seedlots were JT35 from Forari Efate and MT32 from Maewo with mean volume of 0.07 m3. Study reveals that there is a great potential among provenances and families for further improvement and to establish breeding programme to breed whitewood for higher quantity and better timber quality.

Seed germination and seedling development in Taro (Colocasia esculenta)

Two taro (Colocasia esculenta (L.) Schott var. esculenta) cultivars from Fiji and Papua New Guinea were grown at the University of the South Pacific, Laucala Campus, Fiji to produce seeds for seed storage experiments. Gibberellic acid at a 500ppm concentration was used to induce flowering. Very few flowering shoots (inflorescence) were observed in the Fiji cultivar and all pollinations were unsuccessful. However the PNG cultivar flowered well and was used to obtain seed after hand pollination. Hand pollination was carried out to ensure seed setting in developing fruits in the inflorescence. Seeds were extracted in the laboratory after harvesting mature inflorescences. Experiments were conducted on seed moisture content, desiccation, germination, seedling development and seed storage behaviour of taro (Colocasia esculenta) seeds. Seed moisture content was determined using oven methods and air-drying. Results demonstrated that taro seeds have a moisture content of 12-13% after air-drying for three to four weeks. Seeds were dried to desired moisture contents in a desiccator over silica gel. After drying to 5% moisture content seed viability was tested by germinating seeds on moist filter paper at room temperature with 65% relative humidity and seven to eight hours day length. Preliminary seed germination tests demonstrated up to 83% germination for seeds with 13% moisture content. Germination occurred within five to seven days. Maximum germination was achieved within 21 days. The highest germination (80%) was achieved with seeds with 12% moisture content. Results indicated there was no relationship between moisture content and seed germination. Normal seedling development and growth was recorded after germination.

Precipitation effect on flowering and propagule setting in mangroves of the family Rhizophoraceae

Fijian seashores are dominated by Rhizophora samoensis (Hochr.), Rhizophora stylosa Griff. and Bruguiera gymnorhiza (L.) Lam. These three species were studied at two locations—western (dry zone) and eastern (wet zone) parts of Viti Levu (the Main Island of Fiji)—over 2 years consisting of a normal-precipitation and a low-precipitation (drought) year. The research was conducted to understand the flowering pattern, propagule development and propagule size at maturity before dispersal from the mother plant. The flowering pattern and number of propagules at maturity were observed to be significantly different among the three species and within species between a normal-precipitation and very low-precipitation (drought) year. In the drought year (1998), the number of flowers produced per plant and propagule setting were significantly lower than in the normal-precipitation year (1997) at both locations. Only 1–2% of total flowers in each species became mature propagules in the normal-precipitation year. This percentage was significantly lower in the drought year for all three species. Propagule size (weight, length and girth) was found to be significantly different in the three species. R. stylosa produced the biggest propagules, followed by R. samoensis and B. gymnorhiza. Longer and heavier propagules were recorded in the normal-precipitation year than in the low-precipitation year. Flowering patterns, propagule setting and propagule size at maturity are species specific, while differences within species between two zones could be due to different climatic conditions (the amount of rainfall, relative humidity and temperature regimes) prevailing over the 2 years.

Chromosomal Pairing and Pollen Viability in Rhizophora mangle and Rhizophora stylosa Hybrids

Two prominent mangrove species of Fiji, Rhizophora mangle, Linn. Rhizophora stylosa Griff and their puative hyubrid (R x selala) were analysed for chromosome number and pairing. Both parental species and their hybrid possess a diploid number of (2n) = 36 chromosomes. Regular 18 bivalents were observed in two species but the hybrid lacked proper chromosome pairing during meiosis. Analysis of tetrads showed normal tetrad and microspores development in parental species but very high abnormality in the hybrid. Pollen fertility determined by staining technique and pollen germination technique showed very high pollen viability in both parental species but very low pollen viability in the putative hybrid. Lack of chromosomal homology appears to be contributing to high percentage of non-viable pollen resulting in complete sterility in the putative hybrid.

Sex Ratio in Hawaiian Papaya (Carica papaya L.) Variety ‘Solo’

Fruits from hermaphrodite Hawaiian varieties are of medium size and preferred by consumers all over the world. Seeds obtained from the fruits of selfed hermaphrodite plants produce almost two third hermaphrodite plants and one-third pistillate plants. These plants can not be identified before the onset of flowering. However, there are conflicting reports in scientific literature on sex ratios obtained from selfed seeds from fruits of hermaphrodite plants. Sex ratios of hermaphrodite, pistillate and staminate plants were determined using seeds from selfed hermaphrodite fruits of a Hawaiian papaya (Carica papaya) variety ‘solo’. Bagging flowers on hermaphrodite plants during flowering season to avoid contamination from foreign pollen produced self-seeds. Seeds from fruits of many bagged hermaphrodite flowers were pooled together and grown in large plots. A total of 2633 plants were grown and evaluated for their specific sex at the onset of flowering. Of these 1838 were counted as hermaphrodite, 783 pistillate and only 12 staminate plants. This gave a ratio of 2.34 hermaphrodite plants : 1: pistillate plants ignoring 12 staminate plants. This obtained ratio is in disagreement with earlier reported ratio of 2 hermaphrodite plants : 1 pistillate : 1 non-viable zygotes. However, no viable male progeny was reported from hermaphrodite selfed seeds in earlier studies. One of the explanations for the observed changed ratio could be biased seed selection from the seed lot used for planting.