«Breeding Strategies for the Fruit Crop Japanese Quince (Chaenomeles japonica) Breeding Strategies for the Fruit Crop Japanese Quince (Chaenomeles ...»
Breeding Strategies for the Fruit Crop Japanese Quince (Chaenomeles japonica)
Breeding Strategies for the Fruit Crop Japanese Quince
K. Rumpunena*, D. Kviklysb, S. Kauppinenc, S. Ruisad, P.M.A. Tigerstedtc
Balsgård–Department of Horticultural Plant Breeding, Swedish University of Agricultural Sciences,
Lithuanian Institute of Horticulture, Babtai, Lithuania
Department of Applied Biology, University of Helsinki, Helsinki, Finland
d Dobele Horticultural Plant Breeding Experimental Station, Dobele, Latvia *Correspondence to firstname.lastname@example.org SUMMARY In this paper, an ideotype for the fruit crop Japanese quince (Chaenomeles japonica) is established and traits to be specifically considered for selection and breeding are discussed: adaptation and hardiness, disease resistance, thorns, suckering, growth, rooting, time of ripening, yield, amenability for mechanical harvesting and fruit quality. In addition, test guidelines and descriptors for Chaenomeles species are presented. Short-term and long-term breeding strategies are suggested, based on a study of general and specific combining ability for plant vegetative traits, fruit yield and morphology traits, and fruit biochemistry traits. An efficient breeding strategy for Japanese quince could be based on recurrent selection.
However, extensive test crosses and progeny tests in well-designed field trials should also be considered since some important traits are controlled by additive as well as non-additive genes.
IDEOTYPE FOR THE FRUIT CROP JAPANESE QUINCEIn the beginning of a breeding programme, a preliminary ideotype (Donald 1968) should be explicitly defined, to determine the kind of plant material needed. The ideotype should be redefined continuously, as biological and genetic knowledge accumulates. The ideotype established here for Japanese quince (Chaenomeles japonica) as a fruit crop is based on: 1) available knowledge on variation in plant growth and development, 2) a target area for cultivation in the Baltic countries and southern Scandinavia, 3) organic production methods (no use of pesticides or herbicides), 4) mechanical harvest, and 5) industrial processing. Taking these factors into account, the ideal plant must be locally adapted, tolerant to diseases, erect, not too dense, easy to propagate, high yielding, have few branches and no thorns, produce few root suckers, ripen early and have fruits that drop easily at harvest. In addition, fruit internal quality must satisfy the specific demands of the food industry as regards juice, flavour and dietary fibre.
Adaptation and hardiness Since the species C. japonica is not perfectly adapted to the areas in the Baltic region where fruit production is intended, efforts should be devoted towards increasing local adaptation. Selection of hardy plant material will ensure that a severe winter does not destroy plantations and will promote high annual yields.
A lack of hardiness in the Baltic plant material of Japanese quince has previously been compensated for by selection of plants with a spreading rather than erect growth habit. Thus, a snow-cover could protect K. Rumpunen (Ed.) Japanese Quince – Potential Fruit Crop for Northern Europe the plants from low winter temperatures. Unfortunately, cold winters with insufficient snow cover are common, and a spreading or prostrate growth habit is not compatible with other demands, e.g. weed control, phytosanitation and mechanical harvest.
Disease resistance As Japanese quince becomes more widely cultivated, the crop will probably become more attacked by fungi, which are already a problem in other crops within the Rosaceae. Furthermore, since Japanese quince is a long-lived woody perennial, special attention must be paid to pest and diseases, and the plant material available should be screened for field resistant genotypes. Fungal populations and disease pressure can vary according to environmental conditions at the local site, which must be taken into account when field trials are designed. The most serious damage to fruits and shrubs seems to be caused by Phlyctema vagabunda (fruit spots and fruit rot) and Botrytis cinerea (fruit rot and die-back of twigs) (Rumpunen 2002). There is variation among populations in susceptibility to P. vagabunda, allowing resistance breeding (unpublished results). The unspecific behaviour of B. cinerea instead suggests the use of an avoidance strategy. Since the fungus seems to enter the twigs through remaining fruits in late fall, selection for fruit drop at maturity should reduce growth of grey mould from fruits into shoots and thus reduce die-back damage.
Thorns Thorns are undesirable since they make handling of plants difficult and can also damage fruits during management and harvest. In contrast to many other fruit crops, the development of thorns is an adult character in Japanese quince. Selection cannot be successfully undertaken until the third year since juvenile plants generally lack thorns altogether (Kviklys 1998, Rumpunen 2001).
Suckering The production of root suckers is abundant in many genotypes of Japanese quince and is correlated to shrub density. However, suckering seems to be independent of yield parameters (Kviklys 1998). Selection for a lower number of suckers should therefore not have any negative impact on yield.
Growth Growth can be separated into plant height, plant habit and branching. A high and erect plant with few branches would facilitate mechanical harvest. On a high plant, fruits would also become less contaminated by soil and therefore possibly less infected by fungal diseases. As the shrubs become less branched, they also become less dense. Thus the leaf foliage would dry more quickly, which might decrease attacks from leaf fungi, and more sunlight could reach the fruits, promoting a high internal fruit quality.
Rooting The capacity for softwood cuttings to form roots is an important character, which seems to be predominantly governed by additive genes (Kviklys 1998). Shoots from erect plants are slightly more difficult to root than shoots from spreading plants. The capacity for root formation should be evaluated when promising genotypes are propagated and finally selected for evaluation in comparative trials.
Time of ripening In the Baltic countries and southern Scandinavia, fruit ripening starts in mid-August with a peak in midSeptember. Early ripening is especially important in marginal areas of cultivation, whereas varieties with a different ripening period may be valuable for harvesting and processing. Non-additive gene action (dominance and epistasis) seems to be pronounced for start of ripening (Kviklys 1998), and screenings should therefore be conducted in progenies derived from crosses among many selected parents.
Breeding Strategies for the Fruit Crop Japanese Quince (Chaenomeles japonica) Yield Yield is the best measure of integrated performance (Austin 1993) and at the same time, potential yield sets the limit for profitability. Selection for annual and high yields will integrate a range of physiological characters and plant response to a changing environment, and yield is thus a measure of overall adaptation provided that it is estimated over several years. A yield of 3 kg per plant in the fourth season and 4 kg or more in the fifth season (Rumpunen & Kviklys 2001) is considered relatively high, and should constitute the lower boundary for selection.
Amenability for mechanical harvesting To enable mechanical harvest, the plant should be erect, and fruits should drop easily when the shrub is shaken or when combed off the twigs. Fortunately, considerable variability exists in this trait (unpublished results), which besides being dependent on morphology of fruit and petiole, may also be associated with adaptation. At maturity, a natural fruit drop occurs, but late ripening plants may not develop a functional abscission layer.
Fruit quality Fruit quality can be separated into external and internal characters. Since the Japanese quince fruits are primarily intended for industrial use, appearance is of minor importance. However, fruits should be smooth to facilitate washing. The skin should have a sticky cuticle since this appears to be associated with strong fragrance. Skin bruises due to mechanical harvesting are a problem only when fruits are stored for a longer period. High content of fruit flesh and low content of seeds is desirable since the primary products are juice, aroma and dietary fibre.
Test guidelines and descriptors At present there are no specific UPOV test guidelines or official descriptors available for species in the genus Chaenomeles, either as fruit crops or as ornamental plants. An official list of descriptors would be highly useful, not only when new varieties are submitted for test of distinctness, uniformity and stability, but also when plants are described and core collections set up. Therefore, test guidelines and descriptors were developed and compiled for Chaenomeles species (see Appendix). The suggested test guidelines are based on UPOV test guidelines for apple, pear and quince.
GENETIC CONTROL OF TRAITS IN JAPANESE QUINCEA prerequisite for development of efficient breeding strategies is knowledge about the mating system and the mode of inheritance of specific traits (Moreno-González & Cubero 1993). Simple selection of parents based on their phenotypes is efficient only for highly heritable traits (Falconer & Mackay 1996). Therefore, different methods based on prediction of breeding values (Tancred et al. 1995, Durel et al. 1998, de Souza & Byrne 2000) and based on progeny testing (Nyquist 1991, Simmonds 1996, Oraguzie et al.
2001) have been developed. For this purpose, estimates of combining ability are particularly useful (Griffing 1956, Falconer & Mackay 1996). The presence of significant general combining ability (GCA) and lack of significant specific combining ability (SCA) indicates that the trait studied is mainly governed by additive gene action. The presence of significant differences in specific combining ability indicates that the trait is also in part attributable to non-additive gene action (dominance and epistasis). These estimates can thus provide information on patterns of inheritance of various traits and make it possible to predict the performance of progenies in controlled crossings. When additive effects predominate, parents for a breeding programme based on controlled crosses can be selected on the basis of their phenotypic (but preferably on their genotypic) performance. When non-additive effects are also important, selection of parents for creation of breeding populations should be based on progeny tests.
K. Rumpunen (Ed.) Japanese Quince – Potential Fruit Crop for Northern Europe
Despite the above-mentioned benefits, few quantitative genetic studies have been conducted in fruit crops (for references, see Durel et al. 1998). This is partly because many fruit crops have a long juvenile period and in applied breeding, crosses are not designed for genetic studies, plants are not randomised, and records of complete progenies are seldom kept. However, the short juvenile stage and the moderate plant size facilitate genetic studies of Japanese quince.
Phenotypic variation and patterns of inheritance of several plant and fruit traits have been studied in Japanese quince (Rumpunen & Kviklys 2002). Plants with contrasting characters were selected in seedpropagated commercial orchards in Lithuania, and crossed. Fourteen hybrid families were obtained with a total of 684 seedlings, for which five plant vegetative traits, eight fruit yield and morphology traits, and five fruit biochemistry traits were evaluated over seven years. General and specific combining ability were estimated and correlation coefficients were calculated among traits.
Inheritance of thorns When thornless plants were inter-crossed, very few thorny plants were obtained in the progeny (4.8%).
When thorny plants were inter-crossed, 65.7 % of the progeny became thorny, whereas crossing thorny plants with thornless plants produced 54.4% thorny offspring (Table 1). This suggests that thorniness is controlled by a single dominantly inherited gene, and by some modifiers.
Table 1. Segregation for thorns in 14 offspring families of Japanese quince (C.
japonica) divided into four groups according to cross combination. The plants were scored in four classes: no thorns (0), very few thorns (1), few thorns (2) and many thorns (3) (Rumpunen 2001).
Table 2. Pearson correlation coefficients, r, for yield traits and accumulated yield 1996–2000 (ACY96–00), based on single plant estimates and on family means, respectively.
Number of counts is given within parenthesis and correlation coefficients higher than 0.5 are printed in bold (Rumpunen 2001).
ns = non-significant, *** p 0.001 Yield A short juvenile period and annual yields are two valuable features of Japanese quince. Previously it was shown that non-additive effects were pronounced, e.g. for onset of bearing, onset of ripening and yield (Kviklys 1998). Reliable estimates of potential yield were available from three years of harvesting data when based on single plants, and from only two years of observations when based on family means (Table 2). A significant SCA detected in some years for annual yield and accumulated yield, respectively, indicates that not only additive genes but also non-additive genes are important for this trait (Table 3).
Plant and fruit morphology Plant vegetative traits (branching, density, plant habit and height) seem to be primarily controlled by additive genes in Japanese quince as inferred from significant GCA estimates. However, for plant habit and height, non-additive genes are also important (Table 3).
Fruit number, fruit weight, fruit flesh, seed weight and number of seed chambers seem to be primarily governed by additive genes. A significant SCA obtained for fruit weight in one year shows that variation in the environment may also influence the perceived pattern of gene action (Table 3).