Anton Ivancic

Genome size analysis in the genus Cucurbita and its use for determination of interspecific hybrids obtained using the embryo-rescue technique

Abstract The investigation includes the analysis of genome sizes of 11 Cucurbita species (some represented by several botanical varieties). In the majority of species, the genome size was measured for the first time. Values obtained by flow cytometry were based on propidium iodide (PI) staining technique. In contrast to the uniform chromosome number, the genome size differences within this genus appeared to be large, 2C values ranging from 0.686 pg in C. foetidissima to 0.933 in C. ficifolia. PI determined genome sizes of five cultivated species were 0.864 pg (C. pepo), 0.887 pg (C. maxima), 0.933 pg (C. ficifolia), 0.708 pg (C. moschata) and 0.748 pg (C. argyrosperma). The investigation also included several interspecific crosses among cultivated species, using embryo rescue technique. F1 hybrid plants were obtained from crosses: C. maxima×C. pepo (and vice versa), C. pepo×C. moschata, C. ficifolia×C. maxima, (C. maxima×C. moschata)×C. pepo, C. argyrosperma×C. moschata (and vice versa). The formation of plantlets in the last combination, where C. moschata was used as the female parent, had not been previously reported. The interspecific origin of regenerants was confirmed by evaluating relative nuclear DNA content, estimated by DAPI staining. In all hybrid combinations, the relative nuclear DNA contents in interspecific hybrids was intermediate and differed significantly from those determined in parental species. The results show that differences in genome size within the genus Cucurbita are big enough to be used efficiently in determination of interspecific hybrids.

Development of visual tools for selecting qualitative corm characteristics of taro (Colocasia esculenta (L.) Schott)

Taro (Colocasia esculenta (L.) Schott) is an allogamous and polymorphic species with thousands of cultivars. Tremendous morphological variation can be created by artificial genetic recombination. The breeding of taro is expensive, especially when the breeders have to deal with large populations of 10 000 or more individuals. One of the most efficient ways to improve the breeding efficiency is to start selection in an early stage of development, without uprooting the plants, which usually takes 15 months after the germination of seeds. Such an approach has been considered for determining taro corm flesh and corm fibre colours, as these traits are very important for marketing. In the present study, the phenotypic correlation analysis shows that most of the colours of the corm flesh and corm fibres can be determined by scoring the colour of the petiole base and the colour of the lower part of the petiole (2–3 mm above the base). This can be done in an early stage of development and speeds up the recurrent selection process.

Variation of mineral composition in different parts of taro (Colocasia esculenta) corms.

Taro (Colocasia esculenta) is an important root crop in the humid tropics and a valuable source of essential mineral nutrients. In the presented study, we compared the mineral compositions of four main parts of taro corm: the upper, marginal, central and lower (basal) parts. The freeze-dried taro samples were analysed for eleven minerals (K, P, Mg, Ca, Zn, Fe, Mn, Cu, Cd, Pb and Cr). The upper part, which plays a critical role in vegetative propagation based on headsets, contained high levels of P, Mg, Zn, Fe, Mn, Cu and Cd. The central part, which is essential for human nutrition, was characterised by higher concentrations of K, P, Mg, Zn, Fe, Cu and Cd. Ca was concentrated in the lower and marginal parts. The effect of the genotype was significant for more than half of the analysed minerals (i.e., Mg, Ca, Zn, Fe, Mn).

Taro and cocoyam

Aroids are an economically important source of food for numerous tropical countries. They are mostly consumed for their corms and cormels but leaves and petioles can also be part of the diet. According to FAO databases (www.fao.org 2007) taro (Colocasia esculenta (L.) Schott) and cocoyam (Xanthosoma sagittifolium (L.) Schott) produce the lowest average yields (6.5 tons/ha) of all root crops. World production in 2006 was approximately 11.9 million fresh tons from 1.8 million hectares but significant taro producers such as India, Bangladesh, Burma, Indonesia, Papua New Guinea, and Cuba do not supply production figures. Since taro production was around 4 million tons in 1961, its cultivation is stable or even growing and follows the global trend of demographic growth. Aroids are considered minor crops but they are a staple food for numerous poor populations from tropical countries.

Hybrid performance in taro (Colocasia esculenta) in relation to genetic dissimilarity of parents

Taro (Colocasia esculenta) breeding, as other root crop breeding, is based on the production and evaluation of large numbers of hybrids. The selection of parents is based on their phenotypic value in the absence of information concerning general combining ability (GCA), specific combining ability (SCA), or genetic distances between varieties. By combining data from heritability trials and from genetic diversity studies conducted with AFLP and SSR markers, we aimed at studying the relationship between hybrid vigour and genetic dissimilarity between parents. The traits studied included number of suckers, corm weight, corm dimensions, and dry matter content. Correlation coefficients between hybrid gain and dissimilarity values were calculated. The prediction of hybrid performance based on the mid-parent value was compared to the prediction based on a modified expression that takes into account the genetic relationships between parents. Correlations were all but one positive but not statistically significant for all traits, with the exception of the number of suckers, when using SSR markers for dissimilarity calculations. Accordingly, the genetic dissimilarities in the prediction of hybrid performances did not increase the correlation between predicted and observed hybrid vigour values. However, large differences were observed among the residual means from the regression between predicted and observed values when using AFLP or SSR markers, mainly due to the much higher polymorphism revealed by the latter. Models need to be further adapted to the type of molecular marker used, since their ability to reveal different rates of polymorphism will have a direct incidence on the calculation of genetic dissimilarities between genotypes. Nevertheless, since SSR markers are more polymorphic and more informative than AFLP markers, they should be preferentially used for these studies. Low genetic dissimilarity of parents yielded weak heterosis effects and future studies need to be conducted by using a broader genetic base. This is the first study assessing the relationship of hybrid vigour with the genetic distances between parents, conducted on a tropical root crop.

Topology of thermogenic tissues of Alocasia macrorrhizos (Araceae) inflorescences.

Thermogenesis and heat generating tissues in inflorescences of the giant taro (Alocasia macrorrhizos (L.) G. Don) were studied from December 2005 to February 2006, on the Island of Espiritu Santo, Vanuatu. Temperatures were recorded in the ambient air, in the peduncle tissue, and on 12 positions within spadices during periods of maximum thermogenic activity, in the early morning hours of the female and male phases. The study showed that there were three thermogenic tissues: the sterile appendix, the fertile male part, and the differentiated sterile area below the fertile male part. During the female phase, heat was generated by the sterile appendix and the differentiated sterile area below the fer- tile male part, the smallest region of the spadix (mean ± SD = 0.86 ± 0.24 cm, 3.17% of the spadix length), and most probably by the fertile male part. Within the spadix, average temperatures gradually increased from the base of the female part and reached the first peak at the midpoint of the differentiated sterile area below the fertile male part (36.11 ± 1.54 8C). After that, they gradually decreased towards the midpoint of the fertile male part and increased again, reaching a second (main) peak at 1/4 of the sterile appendix height (44.83 ± 1.87 8C). From 1/4 to 1/2 of the appendix height they re- mained at more or less the same level, and then they decreased towards the tip of the spadix. During the male phase, heat was generated only within the fertile male part.

Germination and survival of endangered Pulsatilla grandis (ranunculaceae) after artificial seeding, as affected by various disturbances

Pulsatilla grandis is a rare and endangered species in Central Europe. A field experiment was set up to test the effects of disturbances on its germination and survival rates after artificial seeding. Disturbances were simulated by the following treatments: burning, hoeing, and removal of vegetation. The germination percentage decreased rapidly with time, to only 2% in 2-year-old fruits. The germination rate of fresh fruits was the highest in hoed plots (29.2 ± 12.9%), followed by removedvegetation plots (21.8 ± 17.3%) and burned plots (1.8 ± 2.2%). No germination was observed in control plots. The survival rate of seedlings was monitored over the next 5 years. In the year following the treatment, all the seedlings survived in the burned plots; in the hoed and in removed-vegetation plots, survival rates were 38.5 ± 2 and 55 ± 27%, respectively. Approximately half of them were alive after 5 years. Grassland vegetation in burned quadrates recovered very quickly, whereas in other disturbed plots the numbers ...

Genetically controlled branching corms of taro (Colocasia esculenta)

Abstract Branching in taro (Colocasia esculenta) corms is a complex, undesired, and rare trait, which is expressed because of proliferation of lateral buds. The evaluation of the Vanuatu national taro germplasm collection showed that the frequency of this trait was significantly high (9.51 % of the accessions were characterised by genetically controlled branching). Such a high frequency can be considered as an indication of close relationships among the majority of the Vanuatu cultivars. The expression of branching depends on the genetic structure, specific environmental conditions, interactions between the genetic structure and the environment, and interactions between various developmental stages of a particular genotype and the environment. The genetic control is complex and involves the interaction of at least two loci. The present study suggests that the existing genetic diversity of taro in Vanuatu (and probably also in other geographically isolated Pacific areas) is insufficient for a successful long‐term breeding programme and should include introductions from other countries, especially from the centres of diversity.

Morphological variation and reproductive characteristics of wild giant taro (Alocasia macrorrhizos, Araceae) populations in Vanuatu

Abstract This investigation was aimed at understanding the morphological variation and reproductive biology of wild populations of giant taro (Alocasia macrorrhizos) in Vanuatu. It is an aroid species, which grows in vigorous, relatively small and dense populations, consisting of phenotypically uniform or very similar individuals. The most variable traits observed in wild populations are number of inflorescences, number of infructescences per plant, and corm length. These traits are highly variable even within genetically uniform populations and are highly influenced by age differences between plants. Flowering is frequent and most of the plants are highly fertile. However, sexual reproduction is rare due to self‐incompatibility (between plants genetically homogeneous within the same population) and the absence of efficient pollinators. Self‐incompatibility can be partly overcome by repeated self‐pollination. Thermogenesis was studied on a large sample of inflorescences and little variation concerning the thermogenic potential was observed. Our results showed that, despite optimal flowering conditions (concerning pollen fertility, stigma receptivity, and thermogenic potential), propagation of wild Alocasia macrorrhizos populations in Vanuatu was mainly vegetative. Giant taro plants might have been carried beyond the range of their most effective pollinators. Other factors were considered: the presence of numerous earwigs (Labidura truncata) insects within inflorescences, which could have a competing effect with the usual pollinators of giant taro, and the long distances between genetically homogeneous populations.