G. K. Burge

Opportunities for synthetic plant chimeral breeding: Past and future

Many plant periclinal chimeras are selected by horticulturalists due to their distinctive, valuable phenotypes, and because they are relatively stable. Most of these have arisen by induced or spontaneous mutation. Interspecific chimeras have been accidentally produced from graft unions of plants from a wide range of families. Early last century Winkler developed a technique to produce interspecific chimeras from graft unions (graft chimeras). More recently in vitro techniques have been developed to synthesize interspecific and intervarietal chimeras. However, these techniques have only been successful for species in the families Solanaceae and Cruciferae, and rarely assessed on plants in other families. Research is required to improve these techniques or develop new approaches so that the efficiency of chimeral shoot production is improved and the techniques are applicable to plants in a wide range of families. The unique characteristics of interspecific or intervarietal chimeras show the potential of chimeral breeding to produce new cultivars. If chimeral breeding techniques were improved, they could become a standard breeding approach for some horticultural crops.

Interspecific hybridisation betweenLimonium perigrinum Bergius andLimonium purpuratum L.

SummaryInterspecific hybrids betweenLimonium perigrinum andL. purpuratum were obtained usingL. perigrinum as the female parent. No hybrids were produced by the reciprocal cross. Twelve- to 15-day-old embryos were rescued and cultured within their embryo sacs on modified B5 or KM medium. After two to three days the embryos were excised from their embryo sacs and re-plated on to fresh medium. When the embryo-derived plantlets had attained a length of 1 cm they were transferred to a modified MS medium containing BA and NAA for shoot proliferation. Plantlets were transferred to modified MS medium supplemented with IBA for 24 hours for root initiation then to a modified growth-regulator-free MS medium for root growth. After a further 28 days the plantlets were transferred to soil-less medium for acclimatisation. The hybrid characteristics of one of the 15 embryo-derived plants were determined by flow cytometry and by examination of morphological features. The mean DNA contents of 2C nuclei fromL. perigrinum, the hybrid andL. purpuratum were 13.98 pg, 16.81 pg and 19.37 pg, respectively. Mitotic and meiotic chromosome counts fromL. perigrinum andL. purpuratum showed that both parents and their hybrids had identical chromosome numbers (2n=24), and that the species were closely related. Morphological analyses of leaves and flowers showed that the hybrids displayed a number of features intermediate between both parents.

Wide crosses in the Colchicaceae: Sandersonia aurantiaca (Hook.) × Littonia modesta (Hook.)

Intergeneric hybrids were obtained between Sandersonia aurantiaca and Littonia modesta using ovule culture. The embryos were rescued by culturing 14 to 30 day old ovules. The ovules were cultured on modified KM medium for varying lengths of time until they germinated. After germination the embryo-derived-plantlets were transferred to modified growth regulator-free MS medium on which they developed tubers and became quiescent. The quiescent tubers could be successfully transferred to soil. The hybrid nature of both the putative Sandersonia × Littonia and the Littonia × Sandersonia hybrids was indicated by flow cytometry that showed the hybrid plants had a DNA content midway between that of the two parents. Mitotic and meiotic chromosome counts from S. aurantiaca, L. modesta and the hybrids gave chromosome numbers of (2n=) 24, 22 and 23 respectively. Morphological analyses of the leaves and flowers showed that the hybrids displayed features that were intermediate between both parents. Hybrids were male and female sterile. No morphological differences were observed between the two hybrids.

Postharvest treatments to increase water uptake and the vase life of Leptospermum scoparium Forst

Abstract Postharvest stem treatments and vase‐solution treatments were assessed to determine the basis of the short vase‐life of detached Leptospermum scoparium Forst. stems. Stem cutting or heat treatments had little effect on water uptake or vase life. 8‐hydroxyquinoline sulphate (HQS) delayed the decline in wateruptake and leaf moisture content, and extended the vase life by 1–2 days. Cycloheximide (CHI) also extended the vase life by 2 days. However, the water uptake pattern and changes in leaf moisture content were different from those observed with HQS. Although the rate of flower senescence was similar, CHI treatment resulted in a marked reduction in the rate of decline of water uptake and loss of leaf moisture content. Silver thiosulphate pulse treatments had little effect on flower senescence. Sucrose reduced the rate of flower senescence and when combined with HQS extended the vase life from 3 to 9 days. This suggests that the short vase‐life of L. scoparium is the result of both the sugar statu...

Irrigation, sawdust mulch, and Enhance® biocide affects soft rot incidence, and flower and tuber production of calla

Abstract The incidence and severity of soft rot, flower grades, and tuber yields of calla (Zantedeschia spp.) plants were affected by the quantity of water received during the growing season, sawdust mulch, and Enhance® biocide applications to tubers before planting. Incidence of plants with soft rot symptoms increased at a relatively constant rate during the season reaching an average for all treatments of 61% at the end of flowering. Irrigated plus mulched callas had 15% less soft rot than the irrigation without mulch or the mulch without irrigation treatments. Yield of tubers was 90% greater from irrigated plants. Dipping tubers in Enhance® before planting slightly reduced the severity of rotting in harvested tubers from non‐irrigated plants. The total number of flowers was not affected by irrigation but was slightly reduced by sawdust mulch. However, the number of long stemmed flowers was increased 41% by irrigation, to over 1.5 per tuber.

Control of bacterial soft rot of calla (Zantedeschia spp.) by pathogen exclusion, elimination and removal

Abstract The incidence and severity of bacterial soft rot of calla (Zantedeschia spp.) tubers at harvest were substantially reduced by planting method, chemical control measures, and removal of infected plant material. Callas grown using a sawdust‐shadecloth method had fewer soft‐rotted plants and tubers than callas grown in soil. Dipping tubers before planting in an aqueous solution of 0.08% copper hydroxide, 0.12% thiram, plus 0.03% benomyl reduced plant and tuber losses from bacterial soft rot. Drenching plants during the growing season with an aqueous solution of 0.12% thiram, 0.08% copper hydroxide, plus 0.15% quintozene gave further control against rots. Weekly removal of rotting foliage and tubers during the growing season also reduced levels of plant and tuber soft rots. This study has demonstrated that effective control of calla soft rot can be achieved using disease management that combines appropriate pathogen exclusion, elimination, and removal methods.

EFFECTS OF NITROGEN NUTRITION ON SANDERSONIA CUT FLOWER AND TUBER PRODUCTION IN A SOIL-LESS MEDIUM

Abstract The effects of five nitrogen (N) application rates—14.2, 28.4, 56.8, 113.6, and 227.2 g N/ m2 (equivalent to 37.5, 75, 150, 300, and 600 ppm of N as a daily liquid feed), on greenhouse cut flower production and outdoor tuber production in Sandersonia aurantiaca (Hook.) were compared in two experiments using a peat:pumice medium. Stem length and weight declined with increasing N rate. Tuber weight declined slightly along with tuber quality with increasing N rate. High N rates resulted in an increased incidence of tuber disorders including secondary tuber formation and tuber rots. Leaf N concentration increased with N rate to a maximum of 56.8 g N/m2, but tuber N continued to increase (from 0.68 to 2.01% dry weight) with increasing N rate. The effects of the N rates on tuber storage and subsequent cut flower production were assessed at two N rates (28.4 and 113.6 g N/m2) in a third experiment. Leaf nutrient concentrations were not affected when tubers were forced at the two N rates in the third exp...

Display life of Gentiana flowers is cultivar specific and influenced by sucrose, gibberellin, fluoride, and postharvest storage

Abstract Gentiana are developing into a significant New Zealand export cut flower crop. The current investigation was undertaken to describe the postharvest characteristics of the cultivars grown in New Zealand, thereby establishing a baseline for selection of new cultivars with superior postharvest performance. Three cultivars were used in the current postharvest investigation, G. triflora ’Nasu No‐Hakuryo’ (a white flowered cultivar), and two blue flowered cultivars, G. triflora ’Late Blue’ and G. triflora ’ Ashiro No‐Ake’. The postharvest quality of these Gentiana cut flowers is influenced by a number of factors including harvest maturity, pulsing solutions, cultivar, fluoride, and postharvest storage. In particular, pulsing solutions that contain sucrose (2–5%) or gibberellic acid (GA3, 10 μM) extended the vase life of ‘Late Blue’ and enhanced the quality (blue coloration of apical buds) of ‘Ashiro No‐Ake’, but did not improve the postharvest quality of ‘Nasu No‐Hakuryo’. The effectiveness of these solutions is reduced when stems are not subjected to extended periods of postharvest storage, or when stems are harvested at an advanced stage of maturity.

Shoot regeneration from leaf discs of Limonium perigrinum using thidiazuron

Abstract Shoots were regenerated from 12‐mm diameter leaf discs derived from greenhouse plants of Limonium perigrinum (Bergius), with either zeatin or thidiazuron (TDZ), the latter producing five times the number of shoots. After 8 weeks exposure to a modified Murashige and Skoog basal medium (BM) supplemented with 3.0 mg/litre TDZ, an average of 13 shoots/disc formed, 90% of which were ≤ 1 mm long. There was no significant difference in the total number of shoots formed at 1.0–5.0 mg/litre TDZ, however at lower rates (1.0–2.0 mg/litre) a greater proportion of longer shoots (> 1 mm) developed. Shoots regenerated after 8 weeks from leaf discs exposed to BM with TDZ for from 2 h to 6 weeks before being transferred to growth‐regulator‐free medium. A mean of 4.8 shoots/disc formed from the shortest TDZ pulse period, with the majority being longer than 1 mm. Serial sections of discs pulsed with TDZ medium showed many suppressed shoot initials within the new tissue originating from the cut edge of the discs.

The rise and fall of manuka blight scale: a review of the distribution of Eriococcus orariensis (Hemiptera: Eriococcidae) in New Zealand

The decline in abundance and distribution of the manuka blight scale insect, Eriococcus orariensis Hoy, between the 1950s and 1997/99 is described. Manuka blight was discovered about 1937 in the Orari Gorge, Mid-Canterbury, and by 1958 had become widespread throughout New Zealand. Despite intensive searches in 1997/99, the scale was found on only five out of 27 samples of manuka (Leptospermum scoparium) from 23 sites around New Zealand. A dramatic decline of manuka blight scale, and its displacement by the less noxious species, Eriococcus leptospermi Maskell, in a period of little more than 40 years has occurred. This survey shows that in recent years sooty mould is mainly caused by E. leptospermi rather than E. orariensis.