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  • Author or Editor: Kenneth B. McRae x
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Stem elongation rate (SER) in Dendranthema grandiflorum (Ramat.) Kitamura was determined in light and in darkness under various temperature regimes. Stem growth as measured with linear voltage displacement transducers on plants in growth chambers. Under alternating 11-hour days and 13-hour nights, SER was strongly temperature dependent and showed patterns that were characteristic of the particular photoperiod-temperature regime under which the plants were grown. Total daily elongation was similar at constant 18.3C and at 11.5C days and 24C nights, but was much greater at 25.7C days and 12C nights. SER was rhythmic in continuous light with a period of slightly less than 24 hours. In continuous darkness, however, SER declined rapidly and the rhythm disappeared within 11 hours. Low-temperature pulses (a rapid decline from 18.3C to 8.3C) applied for 2, 4, 6, 8, or 11 hours during the day induced an immediate decline in SER followed by a slow recovery and peak shortly after the end of the pulse. Total diurnal stem growth declined with increasing pulse length, although short (2-hour) duration pulses apparently had little effect on growth. The results are discussed in relation to the influence of day and night temperature differentials (DIF) on stem growth in Dendranthema.

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In Fall 2001 in Nova Scotia's Annapolis Valley (Canada), several million kilograms of processing and table-stock potatoes (Solanum tuberosum L.) were affected by a severe “musty” “off” flavor and “off” odor that persisted after cooking. 2,4,6-Trichloroanisole (TCA), a potent musty flavor/odor compound that is not known to be a potato metabolite was detected in samples of three potato lots rejected by consumers. To determine the role and source of TCA in the affected crop, samples of tubers from 30 fields were evaluated, including examination of production inputs and industry estimation of the “off” flavor, expert organoleptic assessment of flavor–odor intensity, and analytical quantitation of the TCA content of affected tubers, followed by a soil challenge to provoke TCA production. Production of “musty” potatoes was associated with unusually hot (>30 °C) soil temperatures during the 2001 growing season, and in some cases with γ-cyclohexane hexachloride (CHC) applied to control soil wireworm (putatively Limonius agonus Say). TCA quantitation and organoleptic assessment were in general agreement. Samples of soils from “idle” fields (no agricultural inputs for at least 8 years) and “production” fields (produced “off”-flavor potatoes in 2001) were subjected to several factors: 1) presence or absence of potato tubers; 2) preheating at 30 °C for 3 days, or no preheating; and followed by 3) no pesticides, or γ-CHC, chlorothalonil, chlorpyrifos, fludioxonil, imidacloprid, or linuron applied singly, or all six pesticides applied together. After incubation for 2 weeks at 22 °C day/14 °C night with a 14-hour photoperiod, solid-phase microextraction/gas chromatographic–mass spectrometric analysis revealed that untreated soils released small quantities of TCA (2.8 mol·kg−1) whereas higher quantities of TCA were present in soils treated with pesticides (3.8–6.6 mol·kg−1). The quantity of TCA released was not significantly affected by the presence or absence of potato tubers, but it was increased by preheating the soil sample, regardless of the other two factors, and by an interaction between pesticides and soil source. The quantity of TCA from both “idle” and “production” soils was highest when γ-CHC was added alone (214% and 284% of checks respectively). TCA production increased in the presence of the other five pesticides applied singly in “production” soils, but not in “idle” soils. Application of the six pesticides together increased TCA in both soils. Such an association of TCA-based “musty” “off” flavor with field soils containing γ-CHC and other pesticides combined with high soil temperature had not been reported previously.

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