Size factors in strawberry fruit

Analysis of data relating to berries of 9 cultivars grown under different conditions indicates that the weight of ripe berries can be accounted for by the general equation

$\text{Berry fresh weight (g)}\text{=}\text{(}\text{Total no. of achenes}\text{? C)F}\text{(}\text{No. of achenes/cm}{}^2\text{of surface}\text{)}$

where C is a numerical adjustment probably due to the non-spherical shape of berries, and F is the weight in g per unit area of tissue which forms the berry, and both may be characteristic of each cultivar under normal conditions.The number of achenes on perfect berries, equal to the number of ovules initiated on the flowers, is closely related to the position of the flower on the inflorescence. Expressing Rank value on the scale 1 : $\text{1}\text{2}$ : $\text{1}\text{4}$ : $\text{1}\text{8}$ for Rank 1 : Rank 2 : Rank 3 : Rank 4, a general equation

$\text{Achene no.}\text{= (K ×}\text{Rank value}\text{) + D}$

can be applied to all cultivars, although K and D may vary between cultivars and to a less extent within a cultivar. If these size factors are in fact basically genetic, a grower may have little scope for influencing berry size except during berry development in the fruiting-season.     

Photosynthetic characteristics and protective mechanisms against photooxidation during high temperature stress in two citrus species

Exposure of Satsuma mandarin (Citrus unshiu Marc.) and Navel orange (Citrus sinensis Osbeck) plants to high temperature (38 °C) led to reductions of the net photosynthetic rate (Pn), the photorespiration rate (Pr), the quantum efficiency CO₂ assimilation (ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$), the maximal photochemical efficiency of PS2 (Fv/Fm), the photochemical quenching (qP) and the quantum efficiency of PS2 photochemistry (Φ_PS2), whereas the minimal fluorescence yield (Fo) and the non-photochemical quenching (qN) increased. Increase in the value of Pr/Pn and ΦPS₂/ΦCO₂${\Phi }_{\text{PS}2}/{\Phi }_{\text{C}{\text{O}}_2}$ was attributed to the greater decrease in Pn and ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$ than Pr and Φ_PS2. In addition, the superoxide radical (O₂⁻) production, the H₂O₂ concentration and the activities of antioxidant enzymes such as the superoxide dismutase (SOD, EC 1.15.1.1), the ascorbate peroxidase (APX, EC 1.11.1.11), the dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the catalase (CAT, EC 1.11.1.6) were raised. On the other hand, the chlorophyll concentration in leaves decreased during high temperature stress. These results suggest that decline in Pn related to inactivation of PS2 reaction centers may be due to the enhanced number of active oxygen species in the citrus leaves. The water–water cycle may play a role in limiting the degree of photodamage caused by high temperature. Lower O₂⁻ production rate, the H₂O₂ concentration and the antioxidant enzymes activity were observed in high temperature tolerant species of citrus. The exogenous active oxygen scavenger ascorbic acid (Asc) enhanced the ability to clear the O₂⁻ in citrus plants, and quicken the recovery of photosynthetic apparatus.     

Water relations between leaf water potential,photosynthesis and agronomic vine response as a tool for establishing thresholds in irrigation scheduling

During the last few years, leaf water potential has been a useful tool in controlling vine water status. However, the time of measurement that could best explain short- and long-term vine responses remains a matter of discussion. The objectives of this work were to study the relationship between vine water status and vine performance and to determine what time of day leaf water potential is best correlated to physiological performance and agronomic vine response. The assay was conducted in Madrid, Spain. Plant material was Cabernet-Sauvignon (Vitis vinifera L.) grafted onto SO₄. Three irrigation treatments were established: T1 was non-irrigated, and T2 and T3 were irrigated with a constant fraction of the ETo, k = 0.45 and 0.2, respectively. Vine water status was monitored through predawn, midmorning and noon leaf water potential. Their relationships with net CO₂ assimilation rate, vegetative growth rate, yield components and must composition at harvest were studied for 3 consecutive years. Shoot growth rate and net CO₂ assimilation rate were better correlated with midmorning and noon leaf water potentials – Ψ_m and Ψ_n – than predawn leaf water potential – Ψ_pd – but all of them were significant. Shoot growth rate was zero for Ψ_pd = −0.48, Ψ_m = −1.12 and Ψ_n = −1.18 MPa. Berry size was better correlated with the water stress integral for predawn (S_Ψpd$S_{{\Psi }_{\text{pd}}}$) although the water stress integral for midmorning (S_Ψm$S_{{\Psi }_{\text{m}}}$) and noon (S_Ψn$S_{{\Psi }_{\text{n}}}$) performed quite well. No relationship was found between the water stress integral and TSS, total acidity or pH. Leaf water potential performed as a good parameter for determining both vine water status and agronomic response, but not for evaluating must composition.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.