Changing sink strengths influence translocation of phosphonate in avocado (Persea americana Mill.) trees

Translocation of phosphonic acid (H3PO3) in cv. Hass avocado trees was studied after trunk injection with 20% H3PO3, formulated as potassium phosphonate, at three stages of tree phenology during the growing season. Initially, translocation was solely acropetal in the xylem, and H3PO3was detected in the leaves 24 h after treatment. Several days after injection, H3PO3 concentration in the bark of trunks and in roots increased, indicating basipetal phloem transport of H3PO3 from leaves. The rate of accumulation and the final concentration of H3PO3in the roots were directly related to the sink strength of the shoot at the time of injection. For example, trunk injection at the beginning of spring growth flush, when renewal shoots were strong sinks, resulted in low H3PO3 root concentrations (25 8g gfw-1 by 30 days after treatment. These results suggest that strategic timing of injections according to phenological events may greatly improve fungicide efficacy when targeting specific organs for protection

The influence of planting density on the production of 'Goldfinger' (Musa spp., AAAB) in the subtropics

'Goldfinger', a tetraploid banana produced from the Fundación Hondureña de Investigación Agrícola (FHIA) breeding program, was released to the Australian industry in 1995. It was promoted as an apple-flavoured dessert banana with resistance to Fusarium wilt race 1 and subtropical race 4, as well as resistance to black and yellow Sigatoka (Mycosphaerella fijiensis and M. musicola, respectively). This study was initiated to provide agronomic information to the banana industry, which was under threat from Fusarium wilt, on a new cultivar which could replace 'Williams' (AAA, Cavendish subgroup) or 'Lady Finger' (AAB, Pome subgroup) in those areas affected by Fusarium wilt. Also few studies had reported on the production characteristics of the new tetraploid hybrids, especially from subtropical areas, and therefore two field sites, one a steep-land farm and the other a level, more productive site, were selected for planting density and spatial arrangement treatments. The optimum density in terms of commercial production, taking into account bunch weight, finger size, length of the production cycle, plant height and ease of management, was 1680 plants/ha on the steep-land site where plants were planted in single rows with 2.5 m × 2.5 m spacings. However on the level site a double-row triangular layout with inter-row distances of 4.5 m to allow vehicular access (1724 plants/ha) gave the best results. With this arrangement plants were in an alternate, triangular arrangement along a row and a spacing of 1.5 m between plants at the points of each triangle and between each block of triangles

Comparison between micropropagated banana (Musa AAA; 'Williams') and conventional planting material during the first 12 months of development

An understanding of the suckering behaviour of micropropagated bananas is important not only in terms of commercial management but also to gain further appreciation of the physiological mechanisms involved in sucker development. Field studies showed that plants of micropropagated banana (Musa sp., AAA, Cavendish subgroup) produced significantly more suckers than plants grown from conventional planting material (sections of the rhizome with a lateral bud, termed bits). However, when bits were established in containers in a glasshouse and grown under the same conditions as micropropagated plants, the differences became less distinct. In fact, height, dry-matter accumulation and leaf area of the mother plants of micropropagated plants was similar to those of plants grown from containerized bits. Plants derived from bits that had been established directly in the field always lagged behind plants grown from the other two sources. The most significant difference between micropropagated plants and those grown from containerized bits was greater leaf area and dry weight of suckers from the micropropagated plants. Suckers with large leaf areas were categorized as water suckers. These differences may be related to root density and point of sucker origin on the rhizome and supports the need to desucker the early flush of new suckers on young micropropagated plants

Selection of new banana varieties for the cool subtropics in Australia

The most destructive disease in the cool subtropics is race 4 Fusarium wilt caused by the root pathogen, Fusarium oxysporum f.sp. cubense (Foc). In many cases whole production areas have or are being destroyed. It was the need to develop Cavendish varieties resistant to Foc that stimulated banana screening and selection programs, as well as non-conventional genetic improvement programs, in Australia, South Africa, Spain and Taiwan. In Brazil, which also has a conventional breeding program, the primary target is to produce a superior AAB dessert banana that is resistant to race 1 Foc. Because of the focus on Foc resistance, selection of varieties better adapted to the subtropics has been a secondary issue. Some unexpected results have come from these selection programs. For instance, Goldfinger (FHIA-01), developed by the Honduran Foundation for Agricultural Research, has been found to be resistant to Foc and Sigatoka (Mycosphaerella fijiensis and M. musicola) but it also shows a remarkable tolerance to the climatic extremes experienced in the cool subtropics. What is even more interesting are indications that the flavour and texture of the fruit develops best in the cool subtropics of New South Wales and Queensland, but not in tropical Queensland. This demonstrates the need to assess genotype x environment interaction for specific traits in different ecological zones within a country. The challenge for the subtropical industries is to develop or select bananas that are better adapted to the climate and pest/disease complexes of that region, but have flavour and characteristics that appeal to consumers. Preferably the fruit should have attributes that are not easily attained in more tropical regions. The introgression of genes may be targeted in some of these programs from cultivars with cold and drought hardiness (ie. Lady Finger (AAB), Mysore (AAB), Ducasse (AAB)). It is also important to study the genetics and heritability of important traits for the subtropics. Results from selection programs in Australia are discussed

Towards the development of a Cavendish banana resistant to race 4 of fusarium wilt: gamma irradiation of micropropagated Dwarf Parfitt (Musa spp., AAA group, Cavendish subgroup)

'Dwarf parfitt', an extra-dwarf Cavendish cultivar with resistance to subtropical race 4 fusarium oxysporum f. sp. cubense 9Foc), was gamma irradiated at a dose of 20 Gy and putative mutants were recovered with improved agronomic characteristics. Further screening of putative mutants for improved yield and fruit size, as well as a degree of resistence to fusarium wilt, led to the selection of a line (DPM25) with improved productivity when grown on soils infested with subtropical race 4 Foc. DPM25 was equal to the industry standard, 'Williams', in every agronomic trait measured and it consistently showed a lower incidence of fusarium wilt. Further improvement of field resistance to race 4 Foc is needed in DPM25 and further cycles of mutation induction and selction is an option discussed

Micropropagated bananas are more susceptible to Fusarium wilt than plants grown from conventional material

The reaction of field-grown micropropagated bananas, Musa cv. Williams (AAA, Cavendish subgroup) and cv. Goldfinger (AAAB, FHIA-01), to subtropical race 4 Fusarium oxysporum f. sp. cubense (Foc) was compared with the reaction of plants grown from conventional planting material (sections of the rhizome, termed bits). Leaf gas exchange of plants was determined, and growth and dry matter accumulation were measured. Comparisons were made among these parameters from shortly after planting, throughout winter, and into spring when a high percentage of the plants started to show external symptoms of fusarium wilt. Micropropagated bananas were significantly more susceptible to race 4 Foc than plants derived from bits. This was irrespective of planting times, cultivars used, or whether the bits had first been established in containers in the glasshouse (as for micropropagated plants) or been planted directly in the field. This greater susceptibility does not appear to be a consequence of differences in maximum photoassimilation rates, greater photoassimilate demand, or lack of carbohydrate reserves once plants became established

Towards the development of a Cavendish banana resistant to race 4 of fusarium wilt: gamma irradiation of micropropagated Dwarf Parfitt (Musa spp., AAA group, Cavendish subgroup)

'Dwarf parfitt', an extra-dwarf Cavendish cultivar with resistance to subtropical race 4 fusarium oxysporum f. sp. cubense 9Foc), was gamma irradiated at a dose of 20 Gy and putative mutants were recovered with improved agronomic characteristics. Further screening of putative mutants for improved yield and fruit size, as well as a degree of resistence to fusarium wilt, led to the selection of a line (DPM25) with improved productivity when grown on soils infested with subtropical race 4 Foc. DPM25 was equal to the industry standard, 'Williams', in every agronomic trait measured and it consistently showed a lower incidence of fusarium wilt. Further improvement of field resistance to race 4 Foc is needed in DPM25 and further cycles of mutation induction and selction is an option discussed

Through Thickness Microstructural and Texture Inhomogeneity Within Al Layers in ARB-Produced Al-Al(Sc) Layered Composite Sheets

© 2015, The Minerals, Metals & Materials Society and ASM International.Alternatively layered composite sheets of commercially pure (99.8 pct purity) aluminum and an Al-0.3wtpctSc alloy (either in the supersaturated solid solution or age-hardened conditions) were generated through accumulative roll bonding for up to 5 cycles. The transverse sections of the sheets were examined to investigate the microstructure and texture inhomogeneities developed during the rolling process. Electron backscatter diffraction and transmission electron microscopy was used for this investigation. It was found that an inhomogeneous microstructure and texture was developed through the aluminum layers of the sheet thickness. The nature of inhomogeneities changes as the ARB bonding progresses to higher cycles. Microstructural inhomogeneities remain prominent in the first ARB cycle and diminish during the subsequent cycles. Texture inhomogeneities appear in different forms as rolling progresses. High frictional shear forces in the surface and in-plane shear forces across bonding interfaces derive these inhomogeneities