Beta section beta : biogeographical patterns of variation, and taxonomy

Field: Agricultural and Biological Sciences (Life Sciences)

In Chapter 1 an account is given of the historical subdivision of the genus Beta and its sections, and the relations of the sections are discussed. Emphasis is given to the taxonomic treatment of wild section Beta by various authors. The Linnaean names B. vulgaris L. and B. maritima L. are lectotypified, resp. neotypified as a basis for a new classification of the section. Based on the experimental evidence described in Chapters 2 and 3 conclusions are drawn with respect to the classification of section Beta. The revision of section Beta in Chapter 1 acknowledges three species, including B. vulgaris, B. macrocarpa and B. patula. B. vulgaris is subdivided in three subspecies. B. vulgaris subsp. vulgaris is preserved for classification of cultivated beets. Wild forms are classified as B. vulgar is subsp. maritima and as B. vulgaris subsp. adanensis. The number of infraspecific taxa in B. vulgaris is extensively reduced. The classification of minor variants in botanical variaties is abandoned.In Chapter 2 morphological similarities and differences between the taxa of Beta section Beta are discussed and the geographical variation of B. vulgaris is analysed. Plants from wide geographical origin are grown under uniform conditions and evaluated simultaneously. Species relationships and geographical relationships are shown through multivariate cluster analysis and principal component analysis of 79 OTUs and 19 morphological variables.In Chapter 3 allelic variation of isozymes in species of section Beta is evaluated. A selection of 76 accessions was surveyed for allozyme variability. A total of 11 isozymes, all polymorphic for at least one locus, were studied. Genetic variability coefficients were calculated based on 59 accessions and 9 loci.In B. vulgaris subsp. maritima the greatest allozyme diversity is met in accessions originating from the Mediterranean Basin. Generally, B. patula, B. vulgaris subsp. vulgaris, and B. vulgaris subsp. adanensis express the same allozymes as B. vulgaris subsp. maritima. B. patula and B. vulgaris subsp. adanensis could be characterised by the expression of specific allozymes at high frequencies. B. macrocarpa has diverged at a number of loci notably Lap1, Acp1, Pgm2 and Px2. Genetic diversity was low in B. macrocarpa (H e = 0.01) and in B. patula (H e = 0.07). In B. vulgaris sensu lato H e = 0.28 or more. Interspecific differences in levels of observed heterozygosity could be related to the breeding system. The taxa B. macrocarpa, B. patula and B. vulgaris subsp. adanensis expressed low levels of observed heterozygosity confirming self-compatibility. A higher level of heterozygotic genotypes pointed to allogamous, reproduction in B. vulgaris subsp. maritima.The presence of common and rare allozymes was investigated. Allozymes more or less restricted to geographical regions were Acp1 -7 (primarily Mediterranean subsp. maritima ), Mdh1 -1 (primarily Greek and Sicilian subsp. maritima en B. macrocarpa ), Lap1 -5 (primarily Greek and Sicilian subsp. maritima ) en Acp1 -2 (subsp. maritima , Atlantic accessions only, and B. patula ). Mdh1-3 was an allozyme with low frequency, but dispersed over the entire distribution area. The distribution of the particular allozyme Acp1 -2 suggested a close relationship of B. patula with Atlantic B. vulgaris subsp. maritima.It was concluded that the quantification of intrapopulational variability and the description of geographical variation patterns has offered useful information for sampling wild beet populations. Regarding B. macrocarpa and B. vulgaris subsp. adanensis it is essential to sample as many populations as possible from as many different environments as possible. In B. vulgaris subsp. maritima genetic diversity is more or less equally divided in individual plants in a population and between neighbouring populations. Differences in genetic diversity between geographical regions are weak.In Chapter 4 the variation in life cycle and the variation in flowering time between accessions of B. vulgaris and affiliated taxa is described. The effect of external parameters on flowering initiation such as vernalization and daylength conditions was evaluated for a number of representative origins. A vernalization requirement was demonstrated for plants from north Atlantic regions. Although vernalization affected bolting in nearly all accessions, it was noted that the flowering response of the north Atlantic accessions upon vernalization was variable: after vernalization flowering was complete only in plants originating from Brittany, France. Plants from the Netherlands and from the Irish south coast responded by incomplete flowering in the season subsequent to vernalization. Irish north coast accessions seemed to be highly insensitive to vernalization, since even bolting plants were absent after vernalization. Thus, vernalization need and sensitivity to vernalization seem to follow a north - south cline.B. macrocarpa , B. vulgaris subsp. maritima , and B. patula bolt readily without vernalization, and show a strongly reduced period of vegetative growth. B. vulgaris subsp. maritima needs long days both for bolting and flowering, B. patula bolts even in short day conditions, but cannot flower in such conditions. B. macrocarpa flowers readily even in short day conditions. B. macrocarpa seems to be the only obligatory annual taxon of section Beta.In Chapter 5 the germination behaviour of Beta species is described in relation to seed dormancy. The expression of dormancy is tested by exposing variously pretreated fruit balls (glomerulae) to different temperature regimes. The germination pattern of Beta vulgaris ssp. maritima is analysed with accessions originating from the north part of the species distribution, and with accessions belonging to the Mediterranean gene pool. Fruit balls of northern accessions, showed optimum germination in the range of higher temperatures 20° to 30°C. Freshly harvested fruit balls of both accessions showed almost no germination at 10° and 15°C. Stratification of fruit balls enhanced gerniination at the lower temperatures. Mediterranean accessions showed no specific optimal germination temperature, but germination was reduced at 30°C in most of the accessions tested. Generally, the Mediterranean accessions were less sensitive to temperature effects on germination.Chapter 5 also describes the germination ecology of B. macrocarpa . Seed dormancy does not seem to be temperature controlled, but instead mechanical fac tors may limit germination in B. macrocarpa . Compared to B. vulgaris s.l. the penetration of moisture in the fruit balls of this species is more difficult, and the operculum is fixed more tightly to the pericarp, preventing easy protrusion of the radicle.In Chapter 6 the variation pattern of a Sicilian Beta germplasm collection is analysed. Accessions from Sicily were grown under controlled conditions and were evaluated morphometrically. Geographical distribution patterns of morphological characters are identified and the putative classification of the collection into coastal and inland populations is reassessed. Between adjacent populations significant variation was found for Petiole length, Leaf length, Leaf width and Biomass, however not one variable unambiguously reflected a geographical pattern. Overall differences between coastal and inland populations were small. Petiole length and rate of generative development were found to be important for distinguishing between these groups. Interferences are drawn on how the collection from Sicily could be rationalized to avoid excessive duplication.