The Dynamics of Growth and Dry Matter Distribution in Cucumber

The dynamics of growth and proportional dry matter distributionbetween the vegetative parts and fruits of cucumber were studieddaily during a growing season. Most of the changes in dailyintegral of total solar radiation were reflected by changesin plant growth rate. Sometimes a time lag of a few days occurred,indicating the plants were adapting to radiation. The proportional dry matter distribution between fruits andvegetative parts showed a cyclic pattern. The daily proportionaldry matter distribution to the fruits varied between 40 and90% of the total dry matter. However, the cumulative dry weightof the fruits was fairly constant at 60% of the cumulative plantdry weight. The daily proportional dry matter distribution did not seemto be linked directly to the climate conditions (temperature,CO₂ concentration, relative humidity or daily light integral).The proportional distribution to the fruits showed a clear positivecorrelation with the fruit load (number and weight of fruits)on a plant. The number of fruits on a plant changed considerablyduring the growing season. This number was limited not by theformation of new fruits but by abortion of fruits within about10 d after flowering. The number of young fruits that did notabort appeared to correlate positively with the growth rateof the vegetative parts. Cucumis sativus (L.), cucumber, biomass allocation, partitioning, vegetative-generative growth, fruit growth, fruit abortion     

Pithiness and Growth of Radish Tubers as Affected by Irradiance and Plant Density

Pithiness in radish tubers (Raphanus sativus L.) is a syndromewhere xylem parenchyma cells die and are filled with air. Featuresassociated with rapid tuber growth such as large cells, greatdistances between strands of vascular tissue and rupture ofxylem vessels have been suggested to induce pithiness. The objectiveof this study was to analyse the extent to which pithiness inradish was related to tuber growth. Growth rates were variedby altering irradiance and plant density. In addition, the relationshipbetween pithiness and tuber growth (length, diameter, freshmass) was investigated in batches of plants grown under identicalconditions. The growth rates of shoot and tuber strongly increased withincreasing inter-plant distance and irradiance. Our resultssuggest a ‘true’ effect of assimilate supply ondry matter partitioning, as not only the ratio between shootand root dry mass, but also the slope of this relationship decreasedwith increasing irradiance and inter-plant distance. Withina treatment the ratio between tuber growth and shoot growthremained constant with plant age. Increase in length of thetuber did not appear to be an important factor in inducing pithiness.Within a batch of plants, a positive correlation between tuberdiameter and pithiness was observed only for tubers smallerthan 14 mm. An increase in both irradiance and inter-plant distanceincreased tuber size (diameter, mass) and pithiness, but theeffects on pithiness could not be ascribed only to differenttuber sizes. Pithiness strongly increased with plant age andit was concluded that pithiness occurred, to a great extent,according to genetic programming. The data showed that for treatmentswhich affect tuber growth, conclusions about their effects onpithiness depend on whether comparisons were made at the sametuber size or the same time, explaining apparent contradictionsin the literature. Raphanus sativus L.; radish; pithiness; genetic programming; cell death; light; plant density; growth rate; dry matter partitioning; shoot; tuber     

Meristem temperature substantially deviates from air temperature even in moderate environments: is the magnitude of this deviation species‐specific?

Meristem temperature (T_meristem) drives plant development but is hardly ever quantified. Instead, air temperature (T_air) is usually used as its approximation. Meristems are enclosed within apical buds. Bud structure and function may differ across species. Therefore, T_meristem may deviate from T_air in a species‐specific way. Environmental variables (air temperature, vapour pressure deficit, radiation, and wind speed) were systematically varied to quantify the response of T_meristem. This response was related to observations of bud structure and transpiration. Tomato and cucumber plants were used as model plants as they are morphologically distinct and usually growing in similar environments. T_meristem substantially deviated from T_air in a species‐specific manner under moderate environments. This deviation ranged between ?2.6 and 3.8 °C in tomato and between ?4.1 and 3.0 °C in cucumber. The lower T_meristem observed in cucumber was linked with the higher transpiration of the bud foliage sheltering the meristem when compared with tomato plants. We here indicate that for properly linking growth and development of plants to temperature in future applications, for instance in climate change scenarios studies, T_meristem should be used instead of T_air, as a species‐specific trait highly reliant on various environmental factors.     

Effects of Sink Demand on Photosynthesis in Cucumber

In Cucumis sativus L. net photosynthesis of leaf number 12 increaseduntil 12 d after its unfolding and then decreased gradually. Sink demand was varied by imposing the number of fruits perplant without changing the number of leaves per plant. Net leafphotosynthesis did not respond to sink demand during the first16 d of fruit growth. Subsequently, a substantial reductionin photosynthesis was found only when all fruits were removed.This reduction was accompanied by a decrease in the rate oftranspiration, indicating a higher stomataL resistance. Neither starch nor mono- and disaccharides accumulated noticeablyat reduced sink demand, suggesting that there was no end-productinhibition of photosynthesis. Dry matter content of the leaves increased and specific leafarea decreased when sink demand was reduced. When modelling cucumber production, effects of sink demand onleaf photosynthesis can be ignored. Key words: Cucumis sativus, photosynthesis, sink-source, sink demand     

Effects of Seed Number on Competition and Dominance among Fruits in Capsicum annuum L.

The effects of seed number on set, development and growth ofa fruit, and on inhibition of later-developed fruits were studiedby varying the pollen load on the stigma of sweet pepper flowers(Capsicum annuum L.). Despite much variation, a linear increasein individual fruit weight with seed number could be observed.Seed number affected the growth rate rather than the growingperiod of fruit. When seed numbers were low, the probabilityof fruit setting was positively related to seed number. However,a relatively low seed number (50–100 seeds/fruit: 20–30%of the maximum seed number) was sufficient for maximal fruitset. An increase in seed number increased the inhibitory effect ofa fruit on set and growth of later-developing fruits. As a result,when pollination treatments were applied to all the flowersof a plant, results could be quite different to those obtainedwhen only a limited number of flowers were treated. Fruit setof the second fruit was reduced by the application of a highpollen load to the first flower, even when the first fruit abortedbefore it had accumulated much dry matter. Our results suggestthat growth inhibition of the second fruit by seed number ofthe first fruit is controlled both by competition for limitedassimilates, as well as by dominance due to the production ofplant growth regulators by the developing fruit. Sweet pepper; Capsicum annuum L.; pollination; fruit set; abortion; abscission; fruit growth; first-fruit dominance; sink strength