| Degressive protective functions, declining productivity and shortage of superior clonesand new varieties for casuarina plantations in coastal areas of southern China are critical issuesthat need to be addressed. Developing novel crossing techniques and continuously providingnew superior clones and varieties of casuarinas with sustainable genetic gain for ecological andeconomic purposes through multi-generation genetic improvement could help address theseissues.In this dissertation, selection of breeding material, reproductive biology, hybridizationtechniques and hybrid progeny test, and long-term breeding program were studied inCasuarina equisetifolia, C. cunninghamiana and C. glauca. Main results were summarized asfollows:(1) Based on the available genetic materials of the three Casuarina species which havebeen planted extensively in China, genetic variation chacteristics of provenances, families andclones were studied, and some important genetic parameters were obtained to carry outmulti-trait index selection. Some superior breeding materials were obtained for implementingfurther cross-breeding program. Provenance and family trials of C. equisetifolia indicated thatthe overall performance of provenances from4broad regions was in the order: Asia IntroducedRegion＞Asia Natural Distribution Region＞Africa Introduced Region＞Australia/PacificNatural Distribution Region. The overall performance of provenances from15countries wereMalaysia＞China＞India＞Guam＞Papua New Guinea＞Thailand＞Vietnam＞Benin＞SriLanka＞Egypt＞Tonga＞Kenya＞Australia＞Philippines＞Vanuatu. Based on10%selectionratio,9superior families were obtained. The mean genetic gains in Height, Diameter at BreastHeight (DBH), Individual Volume (V), Axis Persistence (AP), Stem Straightness (SS) andSurvival Percentage (SP) were9.0%,3.9%,14.8%,1.2%,1.1%and18.2%, respectively. In provenance trial of C. cunninghamiana,3provenances, viz. C11, C08and C20wereconsidered superior provenances based on20%selection ratio, and mean genetic gains in thesix traits were21.7%,25.9%,76.6%,2.8%,10.7%and10.01%, respectively. In provenancetrial of C. glauca,5provenances, viz. G03, G02, G19, G07and G25were selected as superiorprovenances based on20%selection ratio, and mean genetic gains in the six traits were2.1%,1.4%,2.2%,0.2%,0.2%and6.2%, respectively. In clonal trials involving17casuarina clonesconducted at two sites,3clones, viz. No.17,21and20were selected as superior clones basedon20%selection ratio, and mean genetic gains in the six traits were6.5%,4.8%,10.9%,3.7%,1.5%and8.1%, respectively.(2) The reproductive chacteristics of C. equisetifolia, including floral biology, pollinationbiology, mating system, etc. were studied, and some key background knowledges and systemsof reproductive biology of casuarina were obtained.Based on field observations in three sample plots set up in seedling plantations, it wasfound that there was a higher proportion of male than female individuals in all the threeCasuarina species studied. There were obviously overlapping blooming periods among thethree species which suggested potential probability to produce spontaneous hybrids. Someimportant reproductive chacteristics were evolved to ensure reproductive success at the greatestextent, such as large amount of pollens (771-1145) per anther, long longevity of female flowers(28days) when unreceptive, and some floral features adaptive to anemophily pollination. Therewas evidence of pollination limitation (pollination limitation value0.39) when these casuarinaswere subjected to open pollination conditions, which resulted in low fruit set and seed set.According to experiment results, the pollination limitation could be overcome by supplementalartificial pollination. There were no significant differences in cross-compatibility betweenintraspecific and interspecific hybridization, indicating no reproductive isolation among thethree species. In monoecious individuals of C. equisetifolia, results showed that the index ofself-compatibility was0.94, pollen/ovule ratio was about572.5, outcrossing rate was58.3%,and selfing was completely compatible, therefore monoecious individuals of C. equisetifolia should be included in facultative xenogamy category. Selfing seedlings raised in nurseryshowed serious inbreeding depression, implying the necessity to avoid inbreeding throughcontrolling coancestry in the process of cross breeding of casuarinas.(3) Grafting affinities between and within species of Casuarina genus were studied, andgrafting technique was used for dwarfing, flowering promotion, and pot culture of parent trees.A new controlled pollination approach with high efficiency, high safety rate and ease ofoperation was developed. This approach was used to carry out intra-and inter-specifichybridization of casuarina, and hybrid progenies were measured in nursery and in the field.Grafting experiments showed that plus trees could be dwarfed and early floweringpromoted through grafting. The breeding cycle could be shortened by3-4years. It was foundthat the survival of homograft was87.0～91.4%, and heterograft36.0～45.0%, implyinghigher compatibility of homograft than heterograft. Based on the reproductive biologicalcharacteristics of the three Casuarina species, a new controlled pollination technique wasdeveloped. Using the new technique, fruit set and seed set of C. equisetifolia were increasedfrom7.0%to89.9%, and8.1%to51.8%respectively. According to the new technique,lower temperature and humidity environments would be advantageous in maintaining pollenviability. Pollination chamber could overcome pollination limitation by increasing pollendensity and minimizing disadvantageous impacts of external environments on pollination. Allthese factors were favourable for higher fruit set and seed set. Intra-and inter-specificcontrolled hybridization were conducted using controlled pollination technique developedabove, and hybrid progenies were measured in nursery and in the field. Results showed thathybrid progenies originated from selected parents presented better growth performance thancontrol of open-pollated progenies, implying that selected superior parents can improve geneticgains of hybrid progenies.（4）Proposed long-term breeding program of C. equisetifoliaBased on the reproductive biological characteristics, collected breeding materials and thenewly-developed controlled pollination technique coupled with the practical requirement on casuarina improvement, a long-term breeding program for casuarinas was proposed with aparticular focus on C. equisetifolia. In this program, clearly defined breeding objectives,establishment and management of breeding population and nucleus population, mating designsof intra-and inter-specific hybridization and clonal test were included. Finally two types ofplanting materials, improved hybrid seeds and clones, will be obtained for plantationestablishment for ecological protection and timber production purposes. |
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