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Abstract
In James O. Denney’s letter regarding dormancy terminology (HortScience 22:197, Apr. 1987), the last diagram was drawn incorrectly.
Abstract
The points raised in my previous letter (HortScience 21:1096, Oct. 1986) have been discussed with Greg Lang and his colleagues in correspondence and at the XXII International Horticultural Congress (Aug. 1986) in Davis, Calif.
Xenia and metaxenia are phenomena dealing with the effects that pollen from different sources have on certain characteristics exhibited by seeds and fruits in a variety of species. A review of dictionaries, textbooks, and the scientific literature reveals that there is widespread confusion with regard to the nature of these phenomena and how they are to be distinguished. This discussion will attempt to clarify the boundary between these related phenomena by examining both the origins of the terms and our present understanding of the metabolism and anatomy involved. From this perspective, we contend that xenia applies to pollen effects as exhibited in the syngamous parts of ovules, that is, the embryo and endosperm only. Metaxenia applies to such effects found in any structure beyond the embryo and endosperm, this is, in tissues which derive wholly from mother plant material. Metaxenia then encompasses effects found in seed parts such as the nucellus and testa as well as those found in carpels and accessory tissue.
Xenia and metaxenia are phenomena dealing with the effects that pollen from different sources have on certain characteristics exhibited by seeds and fruits in a variety of species. A review of dictionaries, textbooks, and the scientific literature reveals that there is widespread confusion with regard to the nature of these phenomena and how they are to be distinguished. This discussion will attempt to clarify the boundary between these related phenomena by examining both the origins of the terms and our present understanding of the metabolism and anatomy involved. From this perspective, we contend that xenia applies to pollen effects as exhibited in the syngamous parts of ovules, that is, the embryo and endosperm only. Metaxenia applies to such effects found in any structure beyond the embryo and endosperm, this is, in tissues which derive wholly from mother plant material. Metaxenia then encompasses effects found in seed parts such as the nucellus and testa as well as those found in carpels and accessory tissue.
Fruit removal force (FRF) and percent leaf drop (LD) of fruit-bearing olive (Olea europaea L.) shoots were examined 120 hours after being sprayed with ethephon at 600 mg·liter-1 and held under controlled-environmental conditions analogous to those found in the field in California at harvest time in mid-October. FRF was not significantly affected by solution pH, but FRF of all treated shoots was significantly lower than that of the untreated controls. Only at pH 5 was percent LD significantly greater than that of the controls, but, of the shoots treated with ethephon, the lowest percent LD occurred at pH 3. Percent LD after treatment with ethephon at pH 3 was not affected by application time, but FRF was significantly less than the controls' when shoots were treated at 7 am or 12 pm but not at 5 pm or 10 pm. Adding NAA to the ethephon solution raised FRF and adding BA lowered FRF compared to ethephon alone. Adding NAA or BA did not mitigate percent LD significantly. Adding BA advanced anthocyanin production in fruit. Ethephon penetration of rachides was ≈70% that of petioles. Correlation between ethephon penetration of petioles and percent LD was greater than that between penetration of rachides and FRF. Correlation was significant for both tissues only in the 12 pm pH 3 treatment; correlation was also significant for petiole penetration and percent LD at pH 5. Autoradiographic studies of the 14C-ethephon penetration showed no pH effect, greater penetration into petioles than rachides, and that radioactivity was limited largely to intercellular spaces, with accumulation in vascular bundles, especially xylem. Regardless of treatment, FRF and percent LD are negatively correlated (r 2 = 0.615). Mean results to be expected using ethephon as an olive harvest aid under these conditions are an FRF of ≈3 N and a percent LD of ≈15%. The desired low FRF and percent LD were obtained by applying ethephon alone at pH 3 at 7 am. Raising ethephon solution pH does not increase harvest effectiveness. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon), naphthalene acetic acid (NAA), 6-benzylaminopurine (BA).
We studied the effect on fruit and leaf abscission of application of ethephon (ETP) at 600 mg liter-1 on excised fruit-bearing olive (Olea europaea L.) shoots held under controlled conditions of temperature and relative humidity analogous to field conditions during fall harvest. Fruit removal force (FRF) and percent leaf drop (%LD) were quantified. Raising solution pH did not improve harvest effectiveness. %LD was significantly higher than control at pH 5, but not at pH 3 or pH 7; FRF was not significantly affected by pH. %LD was not significantly higher than control in the time-of-application treatments (pH 3 only); FRF was significantly less than control when applied at 7AM or 12 noon, but not at 5PM or 10PM. Addition of NAA to the ETP solution raised FRF and lowered %LD; BA had the opposite effect. BA accelerated anthocyanin production on fruits. Regardless of treatment, FRF and %LD are highly but negatively correlated (r2 = 0.62). Harvest effectiveness of ETP use on olive can be defined as a convergence of decreasing FRF and increasing %LD. Mean values for all ETP treatments were FRF = 3.0 N and %LD = 15%, acceptable values for effective olive harvest. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); naphthalene acetic acid (NAA); 6-benzylaminopurine (BA).
Record low temperatures were experienced in California during the last 10 days of December, 1990. Olive trees in both the Sacramento and San Joaquin Valleys suffered damage from the freeze. The lowest minimum recorded in these areas was -11.6C at Willows (Glenn Co.). Types of damage included death of succulent growing tips, defoliation, bark split, and bark and xylem discoloration. Tree death to the ground was uncommon. Defoliation continued throughout the growing season, and many leaves that persisted became chlorotic. Major outbreaks of olive knot disease caused by Pseudomonas savastanoi were seen in damaged trees, especially in `Manzanillo.' Anatomical studies showed evidence of ice nucleation events in the phloem, xylem, and leaves, but the cambium was usually left intact. Refoliation and healing of bark splits progressed rapidly once growth resumed in the spring, except in cases of olive knot infestation. Cultural practices that predisposed trees to freeze damage were those leading to late-season vegetative growth, namely fall pruning and late or excessive irrigation or fertilization. `Manzanillo' is the least cold-hardy of California cultivars and the most susceptible to olive knot. `Barouni' is the most hardy.
Abstract
Of several temperature variables that have been suggested to account for flowering and fruiting in the olive (Olea europaea L.) only one—days on which the mean temperature is > 12.2°C and < 13.3°—finds significant expression in the climates of olive-producing regions. Study sites show a mean value of 17.1 ± 4.5 of such days in the period from October 1 to May 31 per year. It can be assumed that vernalization leading to flowering in the olive proceeds when active growth has ceased and when progress of the day’s temperature leads through approximately 12.5°. In olive-producing regions, when mean daily mean temperature is approximately 12.5°, mean daily maximum temperature is 18° and mean daily minimum temperature is 7°.