觀音蓮屬植物之栽培及雜交育種

Abstract

觀音蓮屬(Alocasia)植物葉片形態豐富，極具觀賞價值，廣受市場歡迎。目前此屬植物之栽培及育種相關研究甚少，本研究以市場流行之小仙女觀音蓮(A. ‘Bambino’)作為材料，探討環境因子及肥培管理對其生長及光合作用之影響；並以此屬常見之物種/品種為親本，進行雜交授粉觀察後代之葉片性狀表現，以建立有效之栽培管理及雜交育種資訊，供業者、育種家及居家栽培應用。 小仙女觀音蓮於不同日夜溫環境處理，將葉片展開速率與平均溫度進行迴歸分析，結果顯示葉片展開之基礎溫度為11.3℃，平均每展開一片葉所需之溫積值為166℃d。植株外觀表現以25/20及30/25℃處理較佳；低溫15/13及20/15℃處理之葉面積、植株乾重、光合作用等生長指標均顯著低於其他處理；高溫35/30℃處理雖有最大之葉面積，然葉片厚度薄且濃綠程度顯著較低。 小仙女觀音蓮以光度100-300 μmol·m-2·s-1 PPFD (photosynthetic photon flux density)搭配不同強生氏養液(Johnson’s solution)濃度處理，結果顯示未施用養液組之葉片數少且下位葉明顯黃化，其淨光合作用速率、氣孔導度與蒸散作用較低，但有較高之細胞間隙CO2濃度。葉面積、植株乾重及光合作用均隨著養液濃度上升而增加，以每2週施用1次50%-100%之強生氏養液有最佳之生長表現。將pour-through法測得之EC值與植株乾重及淨光合作用速率分別進行迴歸分析，結果顯示小仙女觀音蓮最適生長之介質EC值為1.4-1.8 dS·m-1。 小仙女觀音蓮於光度100-300 μmol·m-2·s-1下栽培約9個月並移入室內環境16週後，各栽培光度處理組於室內均有新葉生成，植株外觀表現及落葉數不具顯著差異，顯示其具有適應低光之能力。於室內低光下生成葉片之葉斑比例較低，然其白脈與綠色葉身對比較強烈，更具觀賞價值。 每週施用0-20 mM N之養液1次，結果顯示小仙女觀音蓮於缺N處理下植株較小，但並無葉片黃化或落葉情形；新生葉片數及植株乾重隨著養液濃度由0 mM N增加至4-8 mM N達到飽和，增加N濃度至12-20 mM則逐漸降低且根系生長受限，然地上部無明顯鹽害徵狀。每2週施用1次含20 mM N銨態氮：硝酸態氮(NH4+:NO3-)為0:100、25:75、50:50、75:25和100:0之養液，結果顯示銨硝比75:25處理之葉面積及植株乾重最高；新生葉片數、葉綠素計讀值及Fv/Fm於各處理間差異不大，故推論小仙女觀音蓮對N型態之偏好不明顯，但以銨硝比75:25之養液處理生長表現較佳。 小仙女觀音蓮每週以頂部澆灌或底部灌溉給予0%-150%之強生氏養液1次，結果顯示新生葉片數、葉面積及植株乾重等生理指標均隨著養液濃度由0%增加至25%-50%達到飽和，濃度更高則表現漸減或無顯著提升；其中以底部灌溉栽培小仙女觀音蓮僅需每週給予25%強生氏養液，即可與頂部澆灌50%強生氏養液之處理有相同之地上部及全株乾重。植株每週給予1次100%-150%強生氏養液之中、下層介質EC值接近或高於1.4 dS·m-1，導致根部生長受阻。底部灌溉植株之葉面積、Fv/Fm、植株乾重等指標均顯著高於頂部澆灌之處理。 以WET Sensor測定介質體積含水量(volumetric water content, VWC)，探討VWC對小仙女觀音蓮生長及光合作用之影響，結果顯示植株外觀及淨光合作用速率等生理指標均隨著VWC由20%提升至70%而增加；20% VWC之Fv/Fm於試驗期間之起伏較大且顯著低於其他處理，其外觀及生長表現最差但並無明顯葉片黃化或落葉情形，顯示觀音蓮為稍耐旱、喜濕之觀葉植物。 噴施不同濃度之GA3於6個觀音蓮物種/品種，結果顯示部分觀音蓮物種/品種雖有提早花期、增加花序數、並集中花期之效果，然各物種/品種間對GA3之敏感度差異甚大，不易藉由GA3處理以集中各物種/品種間之花期。 取市場上13個觀音蓮物種/品種為親本進行雜交授粉，共自交或雜交83個組合，其中20個組合成功授粉並結實，有14個組合獲得自交或雜交後代；共授粉397個花序，有60個花序成功著果，平均授粉成功率15.1%。參試親本中僅汶萊之星觀音蓮(A. azlanii)、甲骨文觀音蓮(A. scalprum)、諾比觀音蓮(A. sanderiana ‘Nobilis’)及姑婆芋(A. odora)作為種子親可成功獲得後代。性狀調查結果顯示觀音蓮屬之葉柄長度及葉形屬於不完全顯性遺傳，其雜交後代之性狀表現介於兩親本之間。葉脈周邊區域凸起、絨面質感、新葉光澤、葉片花青素表現及紫色葉柄均由一對顯性基因所控制。綠脈物種/品種與紅紫脈物種雜交之後代均為綠脈；而白脈之諾比觀音蓮與綠脈物種雜交之後代均為白脈，顯示葉脈顏色之顯性強度是白脈>綠脈>紅紫脈，其中絨葉觀音蓮(A. micholitziana ‘Green Velvet’)之白脈遺傳模式尚待建立。

Alocasias, with various foliage shapes and variegations, have great ornamental value and popularity in the market. However, information on cultivation and breeding of Alocasia is presently limited. This study used a popular cultivar, A. ‘Bambino’, to understand the effects of environmental factors and nutrient managements on growth and photosynthesis in Alocasia. Additionally, leaf chracteristics in seedlings pollinated from Alocasia species/cultivars were investigated to establish effective breeding information for growers and breeders. Plants of A. ‘Bambino’ were grown at various day/night temperatures. Regression analysis between leaf unfolding rate and average temperature indicated that the base temperature for leaf unfolding was 11.3°C, and the thermal time required for the unfolding of each leaf was calculated to be 166 °Cd. Plants grown at 25/20 and 30/25℃ had greater market appeal. In contrast, leaf area, plant dry weight, and photosynthesis at 15/13 and 20/15°C were significantly lower than other treatments. With a higher temperature at 35/30℃, plants produced the largest but thinnest leaves, with the lowest SPAD-502 value. Plants of A. ‘Bambino’ were cultivated under 100-300 μmol·m-2·s-1 PPFD (photosynthetic photon flux density), and were subjected to various Johnson’s solution concentrations. Results showed that plants without fertilization had fewer leaves, with older leaves yellowing, and decreased net photosynthetic rate, stomatal conductance, and transpiration, but higher intercellular CO2 concentrations. Leaf area, plant dry weight, and photosynthesis increased with increasing nutrient solution concentrations. The best growth performance were observed with bi-weekly applications of 50% to 100% Johnson’s solution. Regression analyses of pour-through EC with plant dry weight and net photosynthetic rate indicated that the optimal medium EC range for growth of A. ‘Bambino’ was 1.4-1.8 dS·m-1. Plants of A. ‘Bambino’ were cultivated under 100-300 μmol·m-2·s-1 PPFD for about 9 months and then moved to indoor environment. After 16 weeks, new-grown leaves were observed in all groups, with no significant differences in plant appearance or leaf drop among the cultivated light intensity treatments, indicating that A. ‘Bambino’ can adapt to low-light conditions. The proportion of leaf variegation was lower in leaves grown under indoor emvironments, but the contrast between the white veins and green leaf tissue was more pronounced, with greater ornamental value. Plants of A. ‘Bambino’ were supplied with nutrient solutions containing 0-20 mM N weekly. Results showed that N-deficient plants were smaller but did not exhibit leaf yellowing or drop. Number of new-grown leaves and plant dry weight increased up to 4-8 mM N, then declined gradually. 12-20 mM N resulted in limited root growth, although no visible signs of salt damage appeared in the above-ground parts of the plant. In another experiment, plants were supplied with nutrient solution containing 20 mM N with different ammonium (NH4+) : nitrate (NO3-) ratios (0:100, 25:75, 50:50, 75:25, and 100:0) bi-weekly. Results showed that 75:25 (NH4+ : NO3-) treatment produced the highest leaf area and plant dry weight. There were no significant differences in the number of new-grown leaves, SPAD-502 value, and Fv/Fm among treatments, suggesting that A. ‘Bambino’ did not have a strong preference for N form, while plants with 75:25 (NH4+ : NO3-) had better growth performance. Plants of A. ‘Bambino’ were supplied with 0%-150% Johnson’s solution weekly with top-irrigation or subirrigation. Results showed that the maximum number of new-grown leaves, leaf area, and plant dry weight were obtained at 25%-50% Johnson’s solution, above which then decreased or had no significant improvement. Notably, plants under subirrigation required only a weekly application of 25% Johnson’s solution to achieve similar shoot and plant dry weight compared to 50% Johnson’s solution with top-irrigation. Reduced root growth occurred in 100%-150% Johnson’s solution treatments with EC values at or above 1.4 dS·m-1 in the middle and bottom layers of the medium. Plants with subirrigation demonstrated significantly higher leaf area, Fv/Fm, and plant dry weight compared to top-irrigation treatments. Plants of A. ‘Bambino’ were subjected to different volumetric water content (VWC) treatments to understand the effects of VWC on growth and photosynthesis. Results showed that plant appearance, growth performance and net photosynthetic rate increased as VWC increased from 20% to 70%. The Fv/Fm values in the 20% VWC treatment fluctuated more during the trials and were significantly lower than other treatments. Additionally, plants of 20% VWC had the worst appearance and growth performance, while there was no leaf yellowing or drop, indicating that A. ‘Bambino’ was moderately drought-tolerant but preferred moist growing medium. Six Alocasia species/cultivars were treated with 0, 250, and 500 mg·L-1 gibberellic acid (GA3) to regulate flowering. Results showed that some species/cultivars flowered earlier, increased number of inflorescences, and flowering more simultaneously, but it was diffecult to synchronize flowering times across different Alocasia species/cultivars due to their varied sensitivity to GA3. Thirteen Alocasia species/cultivars were used as parents for cross-pollination experiments. Among a total of 83 cross or self-pollination combinations, 20 combinations successfully pollinated and produced fruits, and 14 combinations successfully yielded seedlings. A total of 397 inflorescences were pollinated, and 60 of which successfully fruited, giving an successful pollination rate of 15.1%. Among these species/cultivars, only A. azlanii, A. scalprum, A. sanderiana ‘Nobilis’, and A. odora were able to produce seedlings when used as seed parents. Inheritance of petiole length and leaf shape in Alocasia exhibited incomplete dominance, with traits in seedlings falling between the two parents. Unevenness of adjacent part of leaf vein, velvety texture, young leaf luster, leaf with anthocyanin expression, and purple petioles were controlled by a single dominant alleles. Progeny from crossing green-veined species/cultivars and crimson purple-veined species expressed green veins. Progeny from crosses between white-veined A. s. ‘Nobilis’ and green-veined species had white veins, indicating that the dominance order for main vein color was white > green > crimson purple. The genetic pattern for white veins in A. micholitziana ‘Green Velvet’ is still being established.