Flowering-size Nerine bowdenii bulbs were sampled from a commercial planting at 2-week intervals from 13 Aug. 1991 to 14 June 1992. They were dissected, and the following variables were recorded: 1) number and dry weight of fully sheathing leaf bases or leaves of each growth unit, 2) length and dry weight of foliage leaves, 3) fresh weight of outermost inflorescence, and 4) dry weight of daughter bulbs. Bulb organs that served as sinks and sources changed as the bulb progressed in its growth and developmental cycle. Before the new foliage provided photosynthates, growth depended on reserves deposited and stored in leaf bases during the preceding seasons. Reserves were used for the development of new leaves (foliage and bases), roots, and daughter bulb enlargement. Once the foliage became the photosynthate source, reserves were stored in old and new leaf bases. The inflorescence became the major sink when elongation of the scape initiated. Thereafter, daughter bulbs became the dominant sinks, receiving photosynthates from the senescence foliage and the reserves stored in leaf bases. The decrease in dry weight of the leaf bases was prominent in bulbs that remained in situ.
Karen I. Theron and Gerard Jacobs
Audrey I. Gerber, Karen I. Theron, and Gerard Jacobs
Inflorescence initiation in Protea cv. Lady Di (P. magnifica Link × P. compacta R. Br.) occurs predominantly on the spring growth flush when it is subtended by one or more previous growth flushes. Mature, over-wintering leaves are essential for induction of flowering in `Lady Di', and are also crucial to the early stages of inflorescence initiation and differentiation. Defoliation before elongation of the spring growth flush was complete prevented flowering, and shoots either remained vegetative or produced inflorescences that aborted. Levels of carbohydrates in the stem and leaves of overwintering shoots were low, and early growth and development of both the spring flush and inflorescence were, therefore, supported by current photosynthates from the mature leaves on the overwintering shoot. Likewise, reserve carbohydrates available in the flowering shoot were insufficient to account for the rapid increase in dry weight during the major portion of growth of the spring flush and inflorescence. This increase occurred after elongation of the spring flush was complete and was supported by current photosynthates from the leaves of the spring flush. Defoliation treatments that did not prevent inflorescence initiation had no effect on inflorescence development or on flowering time.
Audrey I. Gerber, Karen I. Theron, and Gerard Jacobs
The date of pruning affected flowering time of Protea cv. Sylvia (P. eximia × P. susannae) by influencing the flush on which inflorescence initiation occurred, and the harvest could be manipulated to fall within the optimum marketing period for export to Europe. Flowers initiated on the spring flush reached anthesis in January-February, those on the first and second summer flushes in April-May and July-August, respectively, and those on the autumn flush in November-December. Thus, flowering shoots harvested within the optimum marketing period (September to February) initiated inflorescences on the autumn and spring flushes. Because shoots on the spring flush initiated inflorescences readily, many flowering shoots harvested in January and February (following initiation the previous spring) were short and therefore unmarketable. For commercial production, pruning in July is recommended to allow harvest in October-December of the following year. Since the vegetative and reproductive cycles necessary to produce inflorescences on long stems span more than a year, a biennial cropping system is recommended.
Audrey I. Gerber, Karen I. Theron, and Gerard Jacobs
Protea L. sp. can be assigned to groups according to similar times of flower initiation and harvest. The stages occurring during flower initiation and their synchrony relative to shoot growth were investigated for three cultivars when flower initiation occurred on the spring growth flush. For all three cultivars, the spring flush was preformed and enclosed in the apical bud before spring budbreak. During elongation of the spring flush, the apical meristem produced floral primordia which differentiated into involucral bracts. After completion of the spring flush, meristematic activity continued and produced floral bracts with florets in their axils. The different cultivars were characterized by differences or similarities in the time of budbreak, and the rates of shoot growth, appendage formation, and flower development. Insight into the time of flower initiation relative to vegetative growth could be useful in making management decisions, as well as forming a basis for manipulation of the flowering process.
Willem J. Steyn, Samuel F. Ungerer, and Karen I. Theron
The persimmon (Diospyros kaki Thunb.) cultivar Triumph is prone to poor fruit set, particularly in young orchards, in both Israel and South Africa where it is mostly grown. Two applications of 20 mg·L−1 gibberellic acid (GA3) at 30% and 70% full bloom (FB) are recommended as the industry norm to increase fruit set, but results obtained are often unsatisfactory. We conducted experiments during the 2005–06 and 2006–07 seasons in a young orchard (less than 5 years old) and a full-bearing orchard to determine the efficacy of GA3 application and scoring or girdling during FB to increase fruit set and yield in ‘Triumph’ persimmon. We also established the effect of 2005–06 treatments on return bloom in 2006–07. Although GA3 treatments were ineffective in increasing fruit set and reduced cumulative yield over the two seasons as a result of a reduction in return bloom, scoring increased the cumulative yield by 50% compared with the untreated control and by 92% compared with GA3 application in the young orchard. In the full-bearing orchard, scoring or girdling increased the cumulative yield over the 2005–06 and 2006–07 seasons by 52% compared with the industry standard GA3 application and by 22% compared with trees that received scoring/girdling in addition to GA3. Hence, scoring or girdling did not entirely offset the negative effect of GA3 application on return bloom. The increase in fruit numbers in response to fruit set treatment brought about a reduction in fruit mass. In conclusion, the ineffectiveness of GA3 in increasing fruit set and its negative effect on return bloom do not justify its further use to improve fruit set in young or full-bearing ‘Triumph’ orchards in South Africa. Either scoring or girdling can be used to increase yield but will need to be accompanied by pruning and thinning strategies to achieve adequate fruit size and to prevent the onset of alternate bearing resulting from overcropping.
Hein J. Gerber, Willem J. Steyn, and Karen I. Theron
The European fig cultivars Bourjasotte Noire, Col de Damme Noire, and Noire de Caromb were recently introduced to the Western Cape Province of South Africa. Producers struggle to implement effective commercial practices that will optimize yield of quality fruit. A phenological study was conducted to establish the optimum 1-year-old shoot length to maximize yield. The number of fruit, budbreak, and shoot growth on 1-year-old shoots comprising four length categories (‘Bourjasotte Noire’: 10 to 15, 25 to 40, 50 to 65, and 75+ cm; ‘Col de Damme Noire’ and ‘Noire de Caromb’: 10 to 20, 30 to 50, 60 to 80, and 100+ cm) were evaluated. In ‘Bourjasotte Noire’, all four categories seem to be suited for reproduction in the current season and also provide sufficient new shoot growth to ensure a fair yield the next season. In ‘Col de Damme Noire’, category four seems to be the best 1-year-old shoot length for reproduction both in terms of fruit number and fruit size. However, yield on these shoots may not be optimal the next season, because current-season shoots are too short. It seems that this cultivar will require pruning to stimulate strong new shoot growth that will ensure regular, high yields. In ‘Noire de Caromb’, category one shoots are very productive relative to their length. Categories two and three were also relatively productive, whereas category four was less productive but developed a large number of current-season shoots similar in length to category one that should be productive the next season. These results will allow us to develop pruning strategies to ensure an optimal balance between current-season yield and the development of new fruiting wood to ensure regular, high yields. It also suggests that the three cultivars studied will require differential application of horticultural practices to attain regular, high yields of large fruit.
Ockert P.J. Stander, Karen I. Theron, and Paul J.R. Cronjé
Various mandarin (Citrus reticulata) cultivars are prone to fruit splitting, a physiological disorder that entails cracking of the rind, starting from the stylar end of the fruit, with eventual splitting of the endocarp and abscission of the fruit. On two mandarin cultivars, Marisol and Mor, foliar applications of 2,4-dichlorophenoxyacetic acid (2,4-D), calcium (Ca), and potassium (K) were evaluated over two growing seasons for efficacy to reduce fruit splitting in Paarl, South Africa (lat. 33°69′S, long. 18°95′E). Foliar treatment of 10 mg·L−1 2,4-D directly after physiological fruit drop (APFD) compared with later dates in January and February, either alone or in combination with K, increased rind thickness and reduced fruit splitting of ‘Marisol’ and ‘Mor’ by up to 50%, without negatively affecting internal fruit quality. Treatments increased rind thickness and rind strength throughout fruit development in addition to fruit diameter, length, and growth rate, with no significant effect on rind coarseness. There was a slight reduction in juice content and titratable acidity (TA), but no effect on the total soluble solids (TSS). Application of 2,4-D APFD is thought to increase rind integrity due to a direct strengthening effect on the rind during early stages of fruit development.
Esnath T. Hamadziripi, Karen I. Theron, Magdalena Muller, and Willem J. Steyn
We hypothesized that the microclimate at different positions in the tree canopy may affect the appearance, eating quality, and consumer preference for apple fruit. Hence, the aim of this study was to evaluate the internal and external quality of inner and outer canopy apples in relation to consumer preference for the eating quality and appearance of these fruit. We determined peel color, flesh firmness, percentage starch breakdown, soluble solids concentration (TSS), titratable acidity (TA), and dry matter concentration (DMC) for inner and outer canopy ‘Starking’, ‘Golden Delicious’, and ‘Granny Smith’ from the Ceres region in South Africa in the 2009–10 and 2010–11 seasons. We also determined reducing sugars, total phenolics, and total antioxidant capacity in the 2009–10 season. A trained panel assessed the sensory characteristics of fruit while consumers were asked to indicate their liking for the eating quality and appearance of fruit. Outer canopy fruit of all three cultivars had higher antioxidant capacity, TSS, DMC, lower TA, and were generally sweeter than inner canopy fruit. Consumers could discern eating quality differences and generally preferred the eating quality of outer canopy fruit. The appearance of outer canopy fruit was not preferred in the “green” cultivars, probably as a result of the unfamiliarity of consumers with such fruit. Consumers did, however, prefer the redder outer canopy to the less red inner canopy ‘Starking’ fruit. The redness of ‘Starking’ fruit in this study can therefore be seen as a true signal of eating quality, i.e., the redder the fruit, the better the eating quality, and this would probably apply to other fully red and bicolored apple cultivars. Hence, the classification of red cultivars into different quality classes based on the extent of red color development seems justified from an eating quality perspective. In contrast, blushed outer canopy ‘Granny Smith’ and ‘Golden Delicious’ are culled for aesthetic reasons. It might be possible to develop a niche local market for these blushed fruit based on their better eating quality. Our data were generated in older orchards with trees planted at low density and with large canopies. Planer, two-dimensional canopies are likely to reduce the differences between inner and outer canopy fruit. Differences in macroclimate or in fruit maturity between seasons may also have an overbearing effect on fruit quality parameters compared with canopy microclimatic conditions.
Eugenie-Lien Louw, Eleanor W. Hoffman, Karen I. Theron, and Stephanie J.E. Midgley
The potential impact of increasing temperatures driven by climate change on cultivated Protea cut flower production systems is not known. This study used a biennial pruning system in Protea ‘Pink Ice’ to track the physiological and reproductive responses in comparable phenological stages, but exposed to different seasonally determined temperature conditions. Protea ‘Pink Ice’ generally initiates inflorescences terminally on the spring flush. A limited number of shoots can initiate inflorescences on the preceding autumn flush, leading to an advanced harvesting time compared with that of the spring-initiated inflorescences. In a commercial Protea orchard in Hopefield, South Africa, gas exchange, carbohydrate availability, and vegetative and reproductive growth were compared between the two shoot types in the context of seasonal temperature differences. Leaves of shoots, which initiated inflorescences on the autumn flush, generally had higher light-saturated net carbon dioxide (CO2) assimilation capacities in autumn (April–May) and spring (October–November). There is evidence of a requirement of minimum shoot diameter of 7.6 mm (four- or five-flush shoot), as measured directly above the intercalation between the terminal (uppermost mature flush) and subterminal flush, when the subsequent flush was at budbreak stage during April (autumn) and at least five flushes to be required for floral initiation in Protea ‘Pink Ice’. Spring-initiated inflorescences had a shorter developmental period (4 months) than that of autumn-initiated inflorescences (7 months) and developed into significantly smaller (width) inflorescences with a lower width and dry weight at harvest. These inflorescences were harvested on average a month later compared with autumn-initiated inflorescences. The ambient temperature during inflorescence development played a significant role in the inflorescence growth rate, affecting the time required from visible inflorescence detection to harvest. At the calculated optimum base temperature of 9 °C, autumn-initiated inflorescences required 41,010 growing degree hours (GDH), whereas spring-initiated inflorescences required 35,872 GDH from initiation to anthesis. Under future warmer growing conditions, anticipated decreased size and dry weight of inflorescences may reduce marketability and income for Protea producers.