David J. Woolley

The effect of inter-fruit competition, type of fruiting lateral and time of anthesis on the fruit growth of kiwifruit (Actinidia deliciosa).

The final fruit size of kiwifruit was dependent on seed number, but fruit with few seeds were proportionally smaller if in close proximity to fruit with many seeds. Fruit on the same lateral with equal seed numbers developed to similar final fruit sizes. The final size of a fruit was also partly determined by pre-anthesis factors. Late opening flowers tended to produce small fruit. A predominance (74.3%) of late flowers were found on short (terminating) laterals, while 85.4% of early flowers were carried on long (non-terminating) laterals. Differences in mean fruit size at harvest between fruit developing from early or late flowers on uniform, short laterals were as much as 31 g. This was equivalent to a reduction of about 2 g per day as anthesis was delayed. This difference was independent of fruit seed number, but a significant difference between the size of the ovary of early and late flowers was present at the beginning of fruit development. In addition, fruit produced on long laterals were bigger (10...

Initial alteration of scion architecture by dwarfing apple rootstocks may involve shoot-root-shoot signalling by auxin, gibberellin, and cytokinin

Summary Apple rootstock clones of different vigour were examined to determine how they initially modified the architecture of ‘Royal Gala’ scions following grafting of the composite tree. These modifications were compared with those of gibberellins (GA4+7) and/or benzylaminopurine (BAP) applied to the scion, and an inhibitor of auxin transport [1-N-naphthylphthalamic acid (NPA)] applied to the rootstock stem. By the end of the first year of growth after grafting, the dwarfing (‘M.9’) rootstock had significantly decreased the mean total shoot length and node number of the scion compared with invigorating rootstocks (i.e., ‘MM.106’, ‘M.793’, and ‘Royal Gala’). Similarly, NPA applied to the stem of invigorating rootstocks decreased the total shoot growth of the scion, and the architectural changes imposed most closely resembled those of ‘M.9’. Both treatments increased the proportion of primary and secondary shoots (if present) that terminated growth early, which decreased the final length and node number of these shoot types. Also, NPA and ‘M.9’ decreased the number of secondary shoots that formed. For scions on NPA-treated rootstocks or ‘M.9’, BAP re-instated the formation of secondary shoots, while GA4+7 primarily reduced the proportion of primary and secondary shoots that terminated growth early, thereby increasing their final length and node number. An endogenous signalling mechanism is proposed whereby dwarfing rootstocks reduce the basipetal transport of indole-3-acetic acid (IAA) to the root, thereby decreasing the amount of root-produced cytokinin and gibberellin transported to the scion. At the scion, a limited supply of cytokinin may modify the architecture by decreasing branching, whereas a limited supply of gibberellins may primarily reduce the duration of shoot extension growth.

Patterns of assimilate transport from leaves to fruit within a kiwifruit (Actinidia deliciosa) lateral

SummaryKiwifruit leaves began to export 14C-assimilate when they were 49 to 64% fully expanded. The translocation was bidirectional, but within an intact lateral, assimilates flowed along pathways which linked the fruit on the nth node with its subtending leaf and, at least, with the leaves at nodes n+5 and n+8. However, after the lateral was pruned, the pattern of translocation was altered, so that all the distal leaves supplied each fruit.

Effect of leaf to fruit ratio on fruit growth of kiwifruit (Actinidia deliciosa)

Abstract Fruit size of kiwifruit was not reduced at low leaf-fruit ratios (less than 2:1) on non-girdled laterals because translocation from other parts of the vine could meet any shortfall in the local supply of carbohydrate in the fruiting lateral. However, girdling and 14 C-tracer studies showed that the minimum leaf:fruit ratio that is required to support fruit growth in the kiwifruit lateral, without import of carbohydrate, is 2:1, or approximately 225 cm 2 of leaf area per fruit. Fruit load did not affect the specific leaf weight, photosynthetic rate or stomatal resistance of the leaves on either intact or girdled laterals. Indications of an inhibitory effect on fruit growth by large leaf areas on intact laterals, which was reversed when girdling treatments were applied, may relate to the interactions of growth substances in determining sink strength.

Mechanisms of glyphosate resistance in two perennial ryegrass (Lolium perenne) populations.

BACKGROUND Perennial ryegrass (Lolium perenne) has developed resistance to glyphosate within New Zealand vineyards following many years of herbicide application. The objectives of this work were to confirm resistance within two populations obtained from affected vineyards, and to determine the mechanism of resistance to glyphosate. RESULTS Population O was confirmed to have a 25-fold resistance to glyphosate, whereas population J had a sevenfold resistance. Results of genotyping assays demonstrated a single nucleotide substitution at codon 106 of 5-enolpyruvylshikimate-3-phosphate synthase in population O but not population J. Glyphosate-resistant and glyphosate-susceptible populations did not differ in glyphosate absorption. However, in both resistant populations, much more of the absorbed (14) C-glyphosate remained in the treated leaf than occurred in the susceptible population. Significantly more glyphosate was found in the pseudostem region of susceptible plants compared with resistant plants. CONCLUSION Both target-site and non-target-site mechanisms of glyphosate resistance were found in the perennial ryegrass population with 25-fold resistance, whereas only the non-target-site mechanism of resistance was found in the population with sevenfold resistance. This is the first study of the mechanism of glyphosate resistance in perennial ryegrass.

Retardation of fruit growth of kiwifruit (Actinidia deliciosa) by leaves: interactions with vine performance and seed number

Abstract The growth of fruit with low seed numbers was reduced when there were 8 or more fully, or close to fully, expanded distal leaves on a fruiting lateral. This retardation was found only on young (3–4 year old) vines. The retardation by high leaf numbers was not caused by increased competition for assimilates. There was little inter-fruit competition within a single lateral. Consistent variations in fruit size between selected vines were observed over 3 seasons. These differences in vine performance were not correlated with crop load or leaf-fruit ratio, but were possibly related to factors involving the root system. Significant inhibitory effects of leaves on fruit growth were found only with vines that produced consistently high yields of large fruit.

Temperature effects on dormancy, bud break and spear growth in asparagus (Asparagus officinalis L.)

Summary The effects of the length of chilling, chilling temperature and growing temperature on dormancy of asparagus crown buds and subsequent rates of spear growth were examined. The results showed that prior chilling enhanced bud break at low growing temperatures and stimulated the growth of spears.Thus, chilling should facilitate commercial production by hastening bud break and spear growth rates at lower temperatures. If sufficient chilling was given, the minimum temperature for rapid bud break was approx. 12.5°C for ‘Rutgers Beacon’ and ‘Jersey Giant’, and around 10°C for ‘UC 157’ and ‘Apollo’. The optimum chilling temperature appeared to be closer to 5°C than to 10°C or 2°C for ‘Rutgers Beacon’ plants grown at 12.5°C. Increasing the growing temperature had a significant effect on the relative spear growth rate (RSGR) in all cultivars. Prior chilling had no effect on the RSGR for ‘Dariana’ and ‘Apollo’; but, for ‘UC 157’, chilling plants at 5°C for 5 or 10 weeks increased growth rates at 12.5°C and at 20°C. These results demonstrate that release of bud dormancy and spear growth rates depended not only on the growing temperature, but also, at least in some cultivars at some temperatures, on the duration and temperature of chilling during the previous Winter.

Fruit growth in kiwifruit (Actinidia deliciosa): Patterns of assimilate distribution between laterals

Abstract Different patterns of assimilate translocation were demonstrated in the kiwifruit vine, such that any shortage in the local supply of carbohydrate for fruit growth within a lateral was readily met by surplus carbohydrate from other fruiting or non-fruiting laterals. Assimilate transport occurred in either a basipetal or acropetal direction, depending on the relative positions of the regions of carbohydrate surplus and shortage. Translocation over 7 nodes distance in 1-year-old stems was observed. Fruit on laterals with low leaf-fruit ratios (1:1) imported the most 14C label from neighbouring laterals. The partitioning of 14C assimilate towards these fruit increased with the physical proximity of the laterals. A non-equivalence between girdled and non-girdled shoots was observed. While fruit growth was increased by the presence of non-fruiting laterals in girdled canes, fruit size was reduced by large leaf numbers on non-girdled canes.

Quick tests for detecting glyphosate-resistant Italian and perennial ryegrass

Three quick tests were evaluated for detecting glyphosate-resistant biotypes of Italian ryegrass and perennial ryegrass. Biotypes of these two species were used that were 13.4 and 7.3 times more resistant to glyphosate, respectively, than susceptible biotypes when assessed using a sprayed pot study. One assay exposed germinating seeds of resistant and susceptible populations for 8 days to different concentrations of glyphosate. Measurements of reduction in seedling root growth gave an estimate of resistance magnitude of 10.8 and 8.9 for Italian ryegrass and perennial ryegrass, respectively, similar to that from the sprayed pot study. Two other assays were tested and were able to differentiate resistant and susceptible biotypes. One measured the relative levels of shikimic acid in leaves following exposure to glyphosate; four to seven times more shikimic acid accumulated in glyphosate-susceptible populations of Italian and perennial ryegrass than in resistant populations. The other assay involved growing tillers of the plants in glyphosate solutions and the results showed that at glyphosate concentrations of 10 and 40 mg/L, the plantlets of resistant plants showed negligible visual injury and growth reduction compared with susceptible ones. Results obtained from these assays were not affected by whether the glyphosate formulation used was an isopropylamine salt or potassium salt.

Investigations of how phenoxy‐resistant Carduus nutans biotypes survive herbicide spraying

Abstract Biotypes of nodding thistle (Carduus nutans) have developed within New Zealand that require over six times the normal rate of MCPA, MCPB or 2,4‐D to kill them. Radiolabelled 2,4‐D was applied to both resistant and susceptible nodding thistle plants to investigate the mechanism of resistance. There was no difference in penetration of the 2,4‐D into the foliage of the resistant and susceptible plants. However some minor differences in translocation were detected, with the 2,4‐D apparently less mobile within the resistant plants. These differences were variable and did not fully explain the resistance. Significantly more radioactivity was released from the roots of susceptible plants. There were also small but significant differences in the quantities of radioactivity that could be removed from within the treated plants by ethanol, suggesting more binding within susceptible plants. Significant differences were detected in rates of metabolism of 2,4‐D within the root systems. More radioactivity was present as water‐soluble compounds in the resistant plants than the susceptible ones. Of the ether‐soluble components extracted, about 14 times more 2,4‐D was estimated to be present in susceptible plants than in resistant plants, with chromatography suggesting that compounds in the resistant plants were metabolites of 2,4‐D.