Promotion of seed germination and subsequent seedling growth of loquat (eriobotrya japonica, lindl) by moist-chilling and ga3 applications

Australian avocado orchards are currently planted on seedling rootstocks, which are genetically diverse encompassing genotypes from the three botanical races of Persea americana. This diversity increases the difficulty of getting a uniform outcome from standard management practices. For example, over a 6-year period a 400% difference in yield was measured between ‘Hass’ trees in the same orchard under identical management. Additionally, large differences have been recorded between trees in the susceptibility of fruit developing post harvest rots which negatively impacts on consumers. These differences have been attributed to different rootstocks exerting changes on scion physiology/chemistry. Phytophthora cinnamomi was present in eastern Australia before avocados were introduced in the late 19

Preliminary results from avocado rootstock research in australia

The present experiment aimed at investigating the effects of seed pre-treatment with moist-chilling (mch), GA3, BA or their combinations on seed germination and subsequent drought resistance of the resulting seedlings. The obtained results indicated that increasing the moist-chilling period from 4 to 8 weeks progressively significantly increased the seeds germination percentages (average from 51.2% to 97.2%) and significantly decreased the time to 50% germination (T50) (average from 47days to 27.3 days). The control one (non-moist- chilled seeds) gave the lowest germination percentage (22.6%) and required the highest T50 (72.6 days). The 4 weeks-chilled seeds soaked in BA gave the most satisfactory results as it yielded high germination percentage (average 85.2%), low T50 (average 31.2 days) and saved about at least 4 weeks which would have otherwise being required for moist-chilling of the seeds. The best vegetative characteristics of 2.5-month-old persimmon seedlings were obtained from seeds treated with 8week-moist-chilling solely or with 4week- moist chilling followed by soaking in 20 ppm BA solution for 16 hr. After exposure the subsequent seedlings to 24 days drought period, the results revealed that increasing the moist-chilling period decreased proline content of the seedlings leaves and roots, while increased their leaf resistance to water vapour (LRWV) (9.9, 11.45 & 19.65 sec/cm for 0, 4, 8 weeks of mch, respectively). Generally, seeds pretreated with BA solely gave seedlings with significantly higher root proline content than those of the other treatments, and hence showing more drought resistance features. After the 24 days of drought, leaves of the seedlings resulting from either 4 or 8-weeks-chilled seeds had significantly higher values of chlorophyll (chl a, b) and total soluble carbohydrates (TSC) than those of their corresponding ones resulting from non-chilled seeds. In view of the above findings, the best combination that gave the most satisfactory results was soaking in BA of the seeds which were mois-chilled for 4 weeks.

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The effects of treating persimmon (Diospyros lotus) seeds with moist-chilling and growth regulators on seeds germination, the subsequent seedling characters and their induced drought tolerance.

This study focuses on the soiland water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. cinnamomi suppressive soils and to confirm the involvement of biological processes in suppression. The potential role of cellulase and laminarinase in suppression was investigated and a molecular technique known as length heterogeneity PCR (LH-PCR) was used to analyse the structure and diversity of bacterial and fungal communities in avocado orchard soils that were suppressive and conducive to P. cinnamomi. Four avocado orchards with P. cinnamomi suppressive soils were identified and soils were γ-irradiated to destroy their suppressive capacity, thus confirming biological suppression. Suppression was also partially transferred to γ-irradiated and conducive soils by mixing with 10% suppressive avocado soils. Cellulase and laminarinase activities measured in avocado orchard soils inoculated with P. cinnamomi were not associated with disease severity in lupin seedlings during glasshouse assays involving the same soil samples. In addition, reduced disease severity in avocado seedlings grown in sterile and conducive soils mixed with 10% suppressive soils and inoculated with P. cinnamomi was not associated with cellulase or laminarinase activities in these treatments. When cellulase and laminarinase were added to sterile sand inoculated with P. cinnamomi, disease severity in lupins did not decrease, and the enzyme solutions appeared to have a phytotoxic effect on the plants. Neither suppressive nor conducive soils had characteristic bacterial or fungal community LH-PCR profiles. In addition, LH-PCR indicated that bacterial and fungal community diversity was moderate to high in both suppressive and conducive soils (bacterial Shannon index H′ = 2.99 – 3.01; fungal Shannon index H′ = 3.5 – 3.7). However, minor shifts in bacterial and fungal community structure were observed in response to mixing conducive and irradiated soils with suppressive soils. This was associated with decreased disease severity in avocado seedlings in these treatments.

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Microbial Ecology of Phytophthora cinnamomi Suppressive Soils: A Study of Biological Suppression of P. cinnamomi in Sub-Tropical Avocado Orchards on the East Coast of Australia

Simarouba glauca DC. is oil yielding and medicinally important plant. The seeds of Simarouba glauca imposing hard seed coat physical dormancy and poor in germination. In the present study intact and mechanically broken seeds were soaked in 100 ppm solutions of different plant growth regulators such as 6BA, GA, CCC, SA,Cystein and Methionine for 48 hours. The results reveals that in mechanically broken seeds germination takes place earlier as compared to intact seeds. Further it is evident that GA, SA and 6BAare effective in breaking of physical dormancy of Simarouba glauca which will be beneficial during raising the seedlings in nursery.

Effect of plant growth regulators on seed germination of oil yielding plant simarouba glauca dc.

"Waldin" avocado (Persea americana Mill.) seeds were soaked for 24 hours in concentrations of 0, 250 and 500 ppm gibberellic acid (GA) in lots of 784 seeds each. Moreover, half of the seeds in each lot were left intact and the other half had the apical and basal ends cut off prior to soaking. Cumulative seed germination was re corded 19, 23, 34, 44 and 54 days after planting. Cut seeds at each and all concentraaion(s) of GA snowed higher initial germination than uncut seeds, but the differences dis appeared by 34 days after planting. Cut seeds receiving 250 ppm GA showed higher initial germination, but this differ ence also was eliminated in subsequent measurements. Overall, GA treatment caused no practical differences in total germination. Cutting of seeds reduced total germina tion significantly, probably as a result of embryo damage due to cotyledon separation during cutting, soaking and planting. Nurseries have traditionally experienced problems with avocado propagation caused by a variable germination period of rootstock seeds, which frequently forces the nurseries to extend the propagation period as they wait for late-germinating seedlings to achieve graftable size. The preferred method is to be able to graft everything at one time without having to go back over the propagation beds. Some nurseries cope with this problem by germinating the seeds in seedbeds, then transplanting the seedlings to containers soon after emergence. Thus, propagation can be conducted in sequence on relatively uniform stocks. How ever, the use of a seedbed and transplanting is more labor intensive than seeding directly into containers. Research was initiated in Florida and other areas to enhance the rate of germination of avocado seeds and thus increase seedling uniformity to facilitate once-over propaga tion. Early results indicated that removal of the seed coat of some types of avocados would enhance germination and uniformity (3, 4). However, seed coat removal is difficult and time consuming on many types of avocados and is little used today. Subsequent research showed that cutting off the apical (and sometimes basal) end of the seed facilitated germina tion. Cutting the seed is commonly practiced in avocado propagation today. Work by Leal et al. (4) in Florida centered on the use of gibberellic acid (GA) imbibition of of avocado seeds, with and without the seed coat. 'Waldin' seeds, with and without seed coats, imbibed for 12, 24 and 48 hours in various concentrations of GA, showed enhanced germination and seedling uniformity under laboratory/ greenhouse conditions. Similar results in seedling size and uniformity have been noted in other research with avocados

J. W. Sauls

Papers

Avocado seed germination studies.