No abstract

The contents of the cytokinins zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPA), the combined contents of gibberellins1 + 3 (GA), and the contents of indoleacetic acid (IAA) and abscisic acid (ABA) were measured during the development of the desiccation-sensitive seeds of Avicennia marina (Forssk.) Vierh. During the stage of histodifferentiation the amounts of these plant growth regulators (PGRs) were measured on whole fruits. During the phase of seed growth and reserve accumulation measurements were made on the embryonic axis, cotyledons and pericarp separately. Patterns in the amounts of PGRs present during histodifferentiation were similar to those reported for desiccation-tolerant seeds and it suggested that this process is under similar ‘hormonal’ control in A. marina as in orthodox seeds. Very high contents of cytokinins, particularly ZR, were present in both axes and cotyledons during reserve accumulation. This is thought to be related to the nature of the reserves accumulated (soluble sugars), rather than to the phenomenon of desiccation sensitivity. With the exception of ABA, embryonic contents of PGRs were relatively high at seed shedding, consistent with the rapid germination of this highly recalcitrant seed. ABA contents in the embryo were low during reserve accumulation, but concentrations in the pericarp increased throughout this development stage. ABA in the perticap could act to prevent precocious germination. The low concentrations of ABA in the embryo could be related to the desiccation-sensitivity of the seeds of A. marina.

No abstract

Currently there are only three fungicides registered for use on avocado Two of these (copper and benomyl) are for orchard use and one (prochloraz) is for postharvest use Benomyl has now been withdrawn from sale To test whether onorchard control of rots could be improved some fungicides not currently registered for avocados were screened for inhibition of spore germination and mycelial growth in the laboratory Fungicides tested were azoxystrobin benomyl captan copper hydroxide fluazinam kresoximmethyl prochloraz pyrimethanil and trifl oxystrobin On the basis of these results azoxystrobin benomyl copper hydroxide fluazinam kresoximmethyl and prochloraz were selected for further efficacy testing on the orchard Carbendazim was also tested in the field as a replacement for benomyl Copper hydroxide gave best rot control followed by azoxystrobin and carbendazim

Indole-3-acetic acid (IAA) export and 45Ca uptake by excised avocado flower, fruitlet and shoots from the vegetative flush were determined in conditions which limited transpiration flow to a minimum. Treatments using auxin transport inhibitors were included to ascertain if IAA played a role in the allocation of Ca. IAA levels were determined using radioimmunoassay. IAA export and ~Ca uptake were strongest for the vegetative flush and weaker for the reproductive structures for the first 5 weeks after flowering. The competition for and control of Ca partitioning is discussed.