A major drawback of avocado (Persea americana Mill.) is susceptibility to frosts, which reduces yields and limits its geographic distribution and market growth. Whereas the frost-susceptible cultivar ‘Hass’ leads the global avocado market, cv. ‘Ettinger’, although commercially less important, is considered frost-tolerant. The mechanism behind the greater frost tolerance of ‘Ettinger’ has not yet been elucidated; therefore, the aim of the current study was to evaluate the differences between the frost responses of the two cultivars. The results showed that detached ‘Ettinger’ branches had greater tolerance than ‘Hass’ to controlled frost stress. Tissue browning caused by methyl viologen oxidative cell damage, superoxide accumulation in leaf discs following wounding and browning of cut surfaces in branches were much lower in ‘Ettinger’ than in ‘Hass’, suggesting greater antioxidant activity (AA) in the former. In leaf extracts, AA was significantly higher in ‘Ettinger’ than in ‘Hass’, but osmolarity was similar in the two cultivars. Total phenolics content was significantly higher in ‘Ettinger’ but addition of a protein mask did not significantly reduce AA in either cultivar. Interestingly, following the freezing treatment, AA increased in ‘Ettinger’ and remained almost unchanged in ‘Hass’, while osmolarity was unaffected in either cultivar. These results suggest that the greater frost-tolerance of ‘Ettinger’ than ‘Hass’ is due largely to its greater AA, which springs mainly from a non-enzymatic source, i.e. accumulation of phenolic compounds. Based on the current study, future applications may be developed to minimize frost damage in avocado orchards.

Introduction. Perseaamericana (avocado) fruit is known to be a rich sourceof proteins and minerals, as well as vitamins. Although many biologicalactivities have been reported for avocado fruit, far less attentionhas been paid to the biological properties of its lipid-solublebioactive substances. The aim of this study was to evaluate theantioxidant and antihemolytic activity of lipid-soluble bioactivecompounds of avocado fruit. Materials and methods.Antioxidant and antihemolytic activity of lipid-soluble bioactivecompounds of avocado fruit was assessed by employing different methods.Also, the ability of avocado fruit to protect fluorescein againstoxidant-induced bleaching was evaluated. Results and discussion.The tested sample showed good antioxidant and antihemolytic activities. Therewas no significant difference between the reducing power of lipid-soluble bioactivesubstances in avocado fruits and ascorbic acid (p <0.05). The tested sample showed weak ferrous ion-chelating activity.The sample exhibited moderate hydrogen peroxide scavenging activity, butexhibited good antioxidant activity. Avocado fruit showed very good activityagainst 2,2′-azobis(2-amidinopropane) dihydrochloride- and hydrogenperoxide-induced hemolysis in erythrocytes. Furthermore, it showed goodprotective effects against peroxyl radical-induced bleaching in fluorescein. Conclusion. Lipid-soluble bioactive substances of avocado fruitshowed good activity in all of the studied models.

Introduction. The avocado (Persea americana Mill.) fruit is sensitive to chilling injury (CI) when exposed to low temperatures. High lipid content in avocado pulp makes it prone to oxidation, resulting in rancidity and subsequent production of undesirable flavours and quality loss during storage. Materials and methods. Avocado fruit (cv. Becon) were treated with 1 μL.L-1 1-MCP for 24 h at 20 °C, and thereafter stored at 4 °C for 21 d under low oxygen atmosphere (3.5% O2), followed by transferring to 20 °C for 14 d to simulate the shelf life. The CI index, firmness, peel colour, relative electrical conductivity (EC), respiration, ethylene evolution, malondialdehyde (MDA) content, peroxidase (POD) activity, peroxide value and iodine value were measured throughout the storage period. Results and discussion. The CI incidence and severity of fruit treated with a combination of 1-MCP and low oxygen were significantly lower and delayed compared with the other treatments. The combined application of 1-MCP and low oxygen treatment was effective and delayed the onset of climacteric peaks of respiration and ethylene production. The delay was associated with reductions in fruit softening and cell membrane permeability as expressed by EC. The results of MDA content and POD activity of fruit treated with a combination of 1-MCP and low oxygen were significantly reduced. Moreover, significantly lower peroxide values and higher iodine values suggested that a combination of 1-MCP and low oxygen treatment effectively controlled the lipid oxidation in avocado fruit pulp. Conclusion. Overall, the results support the hypothesis that combined treatment (as compared with either 1-MCP or low oxygen treatment) was the most effective for alleviation of CI, lipid oxidation stability and extending the shelf life of avocado fruit under low temperature storage

Introduction. Canada is an important avocado importer from Mexico. For mostof the harvest season, fruit reach adequate pulp dry matter content, ripen properly and,consequently, quality and shelf life are excellent. However, after January, fruit drymatter content increases and blackened skin occurs. Shipments to Canada containingblackened fruit are rejected because this characteristic is wrongly associated with lowpulp firmness and short shelf life. The objective of our research was to determine theeffect of harvest time and ripening degree on initial quality and shelf life of Hassavocado. Materials and methods. Fruit were harvested from October 2007 toApril 2008, and grouped into five ripening categories according to the degree of blackenedskin. Fruit were then refrigerated for 7 d to simulate shipment to Canada. Thereafter,fruit were stored under simulated market conditions until they reached the edible ripeningstage. Dry matter content was calculated only at the beginning of the storage period whilequantification of weight loss, fruit with blackened skin, pulp firmness, and pulp colorwas done at the beginning of the storage period, at the end of the refrigeration period,and every three days during market conditions. Results and discussion. Drymatter content, skin color and pulp hue angle significantly increased with harvest dateand ripening degree. Weight loss decreased with harvest date but increased with ripeningdegree, while firmness was affected by harvest date but was not associated with ripeningdegree. Conclusion. There is no reason to reject or downgrade blackenedfruit, since quality and shelf life are not affected.

In Cameroon, the demand for hive products is growing. Honey and pollen yields are low in the country, partly because of the poor knowledge of the apicultural value of the flora. To determine the apicultural value of Dichrostachys cinerea (L.), Vitellaria paradoxa Gaertn. F., Persea americana Mill. and Securidaca longepedunculata Fres., Apis mellifera adansonii Latreille activity was observed on the flowers of these plants in Ngaoundéré, from December 2001 to May 2002 and from December 2002 to May 2003. The flowers of each plant species were prospected at least 4 days per month, between 0700 and 1800 h, for recording of the nectar and/or pollen foraging behaviour of A. m. adansonii workers. Results show that A. m. adansonii harvest nectar and pollen of V. paradoxa, P. americana and S. longepedunculata. The flowers of D. cinerea were visited for pollen only. The greatest number of workers foraging simultaneously on a plant varied from 34 (D. cinerea) to 1640 (P. americana). A. m. adansonii workers that visited flowers of a given plant species once remained with this nectar source throughout the observation period. Thus V. paradoxa, P. americana and S. longepedunculata could be cultivated and protected to increase honey production, whereas D. cinerea could enable bee-keepers to increase their pollen production as a hive product. During foraging, A. m. adansonii workers increased pollination possibilities of each of the plant species.

Introduction. In Ethiopia, avocado is cultivated in many traditional homesteads. For the nurseries, there is a need for standardized formulas for potting media constituting locally available sowing media. Materials and methods. Our study was undertaken at the Jimma Agricultural Research Center (Ethiopia) to evaluate the effect of different media types and weights on the emergence and the seedling shoot growth of avocado trees. The study focused on addition of various proportions of locally available organic sources (farmyard manure and coffee pulp) and sand to topsoil. Eight media mixes were prepared. Those media mixes were combined at three media weights [(1.5, 2.5 and 3.5) kg] and studied with a factorial block design completely randomized with four replications. The data on mean days to emergence (Mde) and shoot growth were destructively collected from four sample plants per plot at 30-day intervals (duration) starting from 30 days after emergence (Dae) up to 180 Dae (six months after emergence). An analysis of variance was done at each sampling. Results and discussion. Avocado seeds took about 70 Mde. The different media types significantly influenced the total fresh and dry weight of the seedlings. Plant height, fresh and dry weight and shoot diameters were highly and significantly affected by media type and weight interactions. MT6 (topsoil 3 vol. + farmyard manure 2 vol.) gave a significantly higher total dry weight than MT1 (topsoil 4 vol. + sand 1 vol.) and MT8 (topsoil). Media weights affected all shoot growth characters. As the media weight increased, most shoot growth characters increased. All growth characters were highly influenced by the growth duration, and by the medium weight and growth duration interactions. Conclusion. At the initial growth stages, the dry matter increase was similar on all media weights up to 60 Dae; as the seedlings developed, the effect of higher weights was clearly seen, showing the importance of using larger medium containers for optimizing growth, which is due to the contribution of a larger supply of nutrients and no restriction on root growth. Based on this study, the seedling growth was stabilized between (90 and 120) Dae and responded well to additional nutrients and media weight as growth advanced in the nursery.