Yield Response of Potato (<Emphasis Type="Italic">Solanum tuberosum L</Emphasis>.) Genotypes to Late Blight Caused by <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Uganda

Potato (Solanum tuberosum L.) is a major food and cash crop, mainly grown by small-scale farmers in the highland regions of Uganda. Potato late blight is one of the major diseases limiting production with potential yield losses over 70%, making host resistance a strong element in integrated disease management. This study was carried out to screen and select high yielding potato genotypes with resistance to late blight in Uganda. Forty-eight genotypes, including advanced clones from the population B3C2 of the International Potato Centre, commercial and farmers’ varieties, were evaluated under two environments for two seasons. Trials were laid out in an 8?×?6 alpha lattice design with three replications. Genotypes showed significant differences in yield and resistance to blight. A higher disease severity was observed in Karengyere (56%). The average RAUDPC (= 100 max) across locations indicated that genotypes 395,077.12 and 392,657.8, with disease severity of 12% and 14%, respectively, were the most resistant. Genotypes Victoria (53%) and NKRN59.124 (48%) were the most susceptible. Mean tuber yield under late blight infection was19.8 t ha^?1. The best yielding genotype across sites was 395,112.32 (35.6 t ha^?1) while 394,905.8 (10.3 t ha^?1), yielded the lowest. The mean marketable tuber weight was 8.9 kg with genotypes 395,112.32 and 395,109.34 having the highest marketable weight of 16.5 kg and 15.6 kg respectively. Correlations between yield and yield related parameters were positive (p ≤?0.001), while those between RAUDPC were negative. The following genotypes, 395,112.32, 391,919.3, 393,220.54. 393,077.54, 396,038.107. 392,657.8, Kinigi, 395,014.17, NKRN59.58, NKRK19.17 and 395,011.2, were identified as promising parents for a late blight resistance breeding program. These exhibited high to medium resistance to late blight disease and high yields.     

Survival ofCorynebacterium sepedonicum at freezing and at wide fluctuations between freezing and above-freezing temperatures

The survival ofCorynebacterium sepedonicum, the bacterial ring rot pathogen of potatoes, on burlap surfaces held at constant freezing and above-freezing temperatures and under wide fluctuations of these temperatures was investigated by root-inoculating potato stem cuttings with aqueous suspensions prepared from these surfaces. The pathogen survived and remained infectious on burlap for 53 mo at all constant freezing temperatures, and its infectivity did not diminish throughout this period at either ?20 or ?40°C. At 42 months, viable ring rot bacteria were no longer detected at a constant temperature of 5°C. In a second experiment, ring rot bacteria survived and remained infectious on burlap for 23 months at fluctuating temperatures of ?40 to 5°C and ?40 to 25°C, but only survived for 12 months at 25°C. However, results of this study indicate that wide fluctuations between freezing and above-freezing temperatures caused decreased infectivity of the pathogen.     

Evaluation of frost resistant tuber-bearing solanum hybrids

Frost resistance of interspecific and varietal potato crosses was evaluated at Bogotá, Colombia using intact plants in a programmed low temperature growth cabinet. Plants were exposed to a 2 hour frost during the dark period and the minimum test temperature was successively lowered 1 C on subsequent nights. The foliage was visually scored for damage 10–12 hours after each frost. While most commercial varieties were killed at—2 to—3 C (28 to 26 F), 101 of 121 clones which have been bred specifically for frost resistance survived to at least—5 C (23 F) and some crosses resisted—9 C (16 F) without observable foliar damage. This suggests the possibility of obtaining cultivated varieties from varietal parents of cultivated species such as G. Andigena, G. Phureja, G. Stenotomum,S. ajanhuiri, and others, which are reasonably frost resistant.     

Influence of temperature and length of storage on resistance of potato to tuber rot induced byErwinia chrysanthemi

Tubers of 11 clones ofSolanum tuberosum subsp.andigena (andigena) and 12 cultivars ofS. tuberosum subsp.tuberosum (tuberosum) were inoculated with water suspensions (5.5 × 10⁴ 5.5 × 10⁵, 5.5 × 10⁶ CFU/ml) ofErwinia chrysanthemi. Tubers were inoculated immediately after harvest and after 6 and 16 wk of storage at 4 and 23°C. Tuber rot incidence in andigena and tuberosum increased as inoculum concentration increased. Based on tuber rot severity, clones of andigena were classified as resistant, intermediate, or susceptible and cultivars of tuberosum were classified as intermediate or susceptible. Rot severity increased in all tubers stored at 4°C and in tubers of tuberosum stored at 23°C; rot did not increase in tubers of andigena stored at 23°C. Electrolyte leakage (EL), total sugars (TS), reducing sugars (RS), non-reducing sugars (NRS) and dry matter (DM) were determined in non-inoculated tubers. There was a significant positive correlation between the rate of EL, concentration of RS and tuber rot in andigena and tuberosum. Tuber rot and DM were negatively correlated in tubers of andigena; but they were not correlated in tuberosum. Clones of andigena with low EL, TS, RS, and high DM were resistant to tuber rot, and the incidence of tuber rot in these clones was much less influenced by temperature and length of storage. The influence of temperature and length of storage on susceptibility toE. chrysanthemi may be explained by increased cell membrane permeability; increased leakage of accumulated sugars in potatoes stored at 4°C could favor bacterial proliferation resulting in more disease.     

The use of constant and alternating temperature regimes and tissue culture to obtain PVS—Free potato plants

Growth of 6 potato virus S (PVS)-infected potato clones in tissue culture in temperature regimes alternating between supraoptimal (40°C–45°C) and optimal (25°C) temperatures was compared to incubation of etiolated shoots at constant moderate temperatures (37°C) to obtain virus-free plants by shoot tip culture. Both procedures were effective in obtaining PVS-free propagative material. Virus-free plants were obtained in 5 of 6 clones by the alternating temperatures procedure and in 4 of the 6 clones by the constant 37°C incubation prior to shoot tip isolation. Heat tolerance, virus inactivation, and development of pathogen-free buds from the heat-treated plants depended upon the potato cultivar and the type of culture media in which the tips grew, but these characteristics did not coincide in any clone. The variety Chieftain was the least tolerant to the high temperatures and no virus-free individuals were recovered. White Rose was the most heat resistant, but Russet Burbank resulted with the highest percentage of PVS-free plants. The virus was eliminated from the variety Kennebec only by the alternating temperature treatments. Exposing potato plantlets in the alternating temperature regimes prior to isolation and regeneration of shoot tips was slightly better than the traditional method of incubation of plants at constant moderate temperatures that the plant will withstand and offers a new option in freeing plants of more tenacious viruses.     

Agronomic performance of potato germplasm selected for high resistance to verticillium wilt

A three-year study was conducted from 1991 through 1993 to evaluate the field performance of potato clones that had been selected for resistance to wilt symptom development and stem colonization byVerticillium dahliae. The total yield, size distribution, and specific-gravity of these highly resistant clones were compared with standard cultivars and two parent clones with high Verticillium resistance and high yield, A66107-51 and A68113-4. Two groups of Verticillium resistant germplasm were selected in 1991. One group was the highly resistant progeny from a cross between A66107-51 and A68113-4. The second group consisted of hybrids between wild species accessions with high Verticillium resistance and cultivated diploid and tetraploid germplasm. Twenty-one out of 125 progeny clones from the A66107-51 × A68113-4 cross were highly resistant to Verticillium infection and were tested in yield trials for two years. Another eight selections had high Verticillium resistance but such low yield of seed tubers that they were tested only one year for yield. Eleven of the original 29 highly resistant selections were significantly lower in total yield than Russet Burbank. Only one clone was significantly higher in yield than RB, and none outyielded either of the resistant parents. Reddale and Century Russet had moderate to high Verticillium resistance, respectively. Both outyielded Russet Burbank and were comparable with the high yielding resistant parents. Of 15 interspecific hybrids tested in 1991, only four had sufficient yield to produce seed for yield trials and good wilt resistance after three successive seasons of evaluation. We concluded from this study that selecting at early stages of variety development strictly for Verticillium resistance is likely to be inefficient. Rather, selection should be for yield and other agronomic criteria in Verticillium infested fields.     

High Temperature Modifies Resistance Performances of Rice Varieties to Brown Planthopper,Nilaparvata lugens(Stl)

To investigate the effect of temperature on the resistance characteristics of rice varieties with different resistance genes to brown planthopper(BPH),Nilaparvata lugens(Stl),the resistances of IR26(Bph1)and IR36(bph2)to BPH population in Hangzhou,China were monitored in greenhouse during September in 2007 and 2008 by using the standard seedling screening techniques(SSST)developed by the International Rice Research Institute(IRRI).Furthermore,the changes in resistance of IR26 and IR36 to BPH,soluble sugar and oxalic acid contents in 25-day-old rice plants of susceptible variety TN1 and resistant varieties IR26 and IR36 were detected at five temperatures(22℃,25℃,28℃,31℃ and 34℃).IR26 completely lost resistance both in greenhouse and at the five tested temperatures.IR36 still had moderate resistance at natural temperature,but its resistance decreased gradually when the temperature increased from 25℃ to 34℃,and fully lost its resistance at 31℃ and 34℃.The highest durable resistance of IR26 and IR36 were recorded at 25℃.The soluble sugar content in plants of the three tested rice varieties increased with temperature increase,and the oxalic acid content increased with the temperature increase at first,maximized at 25℃,and then declined.Two-way ANOVA indicated significant effects of temperature and rice variety on contents of soluble sugar and oxalic acid in rice plants.     

Relationship of foliar ozone injury to maturity classification and yield of potatoes

Fifty-nine potato cultivars and selections were planted in replicated plots at two Ohio locations each in 1975 and 1976. Evaluations of ozone “speckle leaf” injury were made during August and yields were recorded in October. A broad range in resistance to ozone injury was noted at both locations with later-maturing entries generally being more resistant. Entries severely injured by ozone had a reduced yield. The relative resistance of most entries was constant in all tests.     

Assessment of the frost sensitivity of wild and cultivated potato species by chlorophyll fluorescence analysis

Summary The potential of the chlorophyll fluoresence technique in screening for frost sensitivity in seedling progenies representing 18 genotypes of wild and cultivated potato from different geographical and altitudinal origins was assessed by measuring the decrease in variable chlorophyll fluorescence (F_var) of terminal leaflets of hardened and non-hardened plants after freezing at −5°C for 60 min and subsequent re-warming to 20°C. The method was rapid and the results obtained agreed well with a visual assessment of frost injury carried out after leaflets had been returned to optimal growth conditions for 72 hours.Solanum tuberosum CPC 3294 originating from Chile was the most frost-sensitive genotype studied andSolanum albicans CPC 3712 from high-altitude regions of Peru, the most frost-resistant. Frost damage increased with length of exposure to frost and this was associated with a reduction of variable fluorescence and quenching capacity of the thylakoid membranes.

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Zusammenfassung An S?mlingsnachkommen, die 18 Genotypen wilder und kultivierter Kartoffelarten aus verschiedenen geographischen Herkünften und H?henlagen repr?sentierten, wurde die Eignung der Chlorophyll-Fluoreszenztechnik zur Prüfung auf Frostempfindlichkeit untersucht, in dem die Abschw?chung bei der variablen Chlorophyll-Fluoreszens (F_var) an den endst?ndigen Fiederbl?ttern abgeh?rteter und nicht-abgeh?rteter Pflanzen nach 60 minütigem Abkühlen auf −5°C und anschliessender Erw?rmung auf +20°C gemessen wurde (Abb. 1). Diese Methode war schnell, und die damit erhaltenen Ergebnisse stimmten gut mit einer visuellen Beurteilung der Frostsch?den nach dem Zurückbringen der Bl?ttchen für 72 Stunden in optimale Wachstumsbedingungen, 15°C/10°C (Tag/Nacht), überein. Die visuelle Beurteilung der Besch?digung basierte auf den Schadsymptomen wie Chlorosen, w?sserigen Flecken und nekrotischen Bereichen, ausgedrückt in Prozenten der beeintr?chtigten Fiederblattfl?che und korrigiert an Hand der nicht-gekühlten Kontrolbl?ttchen. Die aus Chile stammendeSolanum tuberosum CPC 3294 erwies sich als der Genotyp mit der h?chsten Frostempfindlichkeit undSolanum albicans CPC 3712 aus den hohen H?henlagen Perus als derjenige mit der h?chsten Frostresistenz (Tab. 1). Der Frostschaden nahm mit der Dauer der Frosteinwirkung zu und war verbunden mit einer Reduktion der variablen Fluoreszenz und der Quench-Kapazit?t der Thylakoidmembranen (Abb. 3). Diese Ergebnisse weisen darauf hin, dass das starke Zerreissen der Thylakoid-membranen durch das Gefrieren verursacht wird (Tab. 2). Ferner wurde gefunden, dass die 10-t?tige Frostabh?rtung bei 4°C/2°C (Tag/Nacht) vor dem Versuch nur eine geringe Wirkung auf die Reduktion des durch die Thylakoidmembranen entstandenen Schadens hatte, mit Ausnahme verschiedener chilenischer Sorten vonSolanum tuberosum (CPC 5374, CPC 5646, CPC 5643, CPC 3294) (Tab. 1). Die Abbildung 4 zeigt die ?nderungen im F_R (Rate des Fluoreszenzanstiegs) nach dem Gefrieren bei −5°C. Wenn diese Technik auch nicht alle anderen gegenw?rtig verwendeten Frostunter-suchungsmethoden v?llig zu ersetzen vermag, so sollte sie doch von den Pflanzenzüchtern als ein zus?tzliches Instrument betrachtet werden, um bei Pflanzen K?ltesch?den abzusch?tzen.

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Résumé La sensibilité au gel de plantules issues de 18 génotypes comprenant des espèces sauvages et cultivées de pommes de terre est étudiée par mesure de la diminution de fluorescence chlorophyllienne (F_var) des folioles apicales sur des plantes durcies ou non après passage au froid à −5°C pendant 60 minutes suivi d'un réchauffement à 20°C (figure 1). La méthode est rapide et les résultats obtenus sont comparables aux notations visuelles des dégats de gel, lorsque les folioles sont mises en condition optimale de croissance: 15 °C/10 °C (jour/nuit) pendant 72 heures (figure 2). Pour la notation visuelle, les observations portent sur les sympt?mes tels que les chloroses, les poches d'eau et les zones nécrotiques, exprimés en pourcentage de surface endommagée par rapport au témoin non gelé.Solanum tuberosum, CPC 3294, d'origine chilienne, s'avère être le génotype testé le plus sensible etSolanum albicans, CPC 3712, originaire des hauts-plateaux péruviens, le génotype le plus résistant (tableau 1). L'endommagement par le gel augmente avec la durée d'exposition au gel et cela correspond à une diminution de fluorescence et de capacité d'étanchement des membranes thylako?des (figure 3). Ces résultats montrent qu'un éclatement réel des membranes thylako?des est induit pendant le gel (tableau 2). Un durcissement à 4°C/2°C (jour/nuit) pendant 10 jours avant l'expérience a peu d'effet sur le niveau d'endommagement maintenu par les membranes thylako?des, à l'exception de quelques variétés chiliennes deSolanum tuberosum (CPC 5374; CPC 5646; CPC 5643; CPC 3294) (tableau 1). La figure 4 montre les changements de F_R (taux d'augmentation de fluorescence) après le gel à −5°C. Bien que cette technique ne puisse remplacer totalement les méthodes utilisées jusqu'à ce jour, elle peut servir de complément d'analyse dans la recherche de variétés sensibles aux basses températures.

     

Utilizing the frost resistance of diploid solanum species

Introductions of 13 frost-resistant diploid (2n=2x=24)Solanum species (2 non-tuberous) were inter-crossed to produce F₁ hybrids involving two frost resistance sources. Successful F₁ combinations were: (i) inter-crossed to produce hybrids involving 3 to 4 frost resistance sources, (F₁×F₁); and (ii) crossed with haploids (2n=24) of frost-susceptible tetraploid (2n=4x=48)S. tuberosum subsp.tuberosum, (F₁×tbr). Thirty-five of the 75 crosses between the 13 species produced viable seed. The F₁ and F₁×F₁ progenies segregated to yield plants more resistant to freezing temperatures than the parental species. All attempts to cross these hybrids with 24-chromosometbr were successful. Although tuber production improved following the first cross totbr, the frequency of resistant plants decreased approximately 50%. Thus far, all first back-cross attempts, (F₁×tbr)×tbr, have succeeded. Utilizing hybrids synthesized from several sources of frost resistance as the donor parents, and clonal selections of 24-chromosometbr as the recurring parents, may provide a high order of resistance throughout the backcrossing program and implement selection of frost-resistant, long-day tuberizing parental stocks acceptable to the potato breeder.     

Latent infection of potato tubers byPseudomonas solanacearum

Strains ofPseudomonas solanacearum differed in their ability to infect tubers of different resistant potato clones grown in infested soil. When eight resistant clones (Solanum phureja orS.phureja ×S. tuberosum hybrids) were grown at 24–28°C in soil infested with a race 1 or a race 3 strain of the bacterium, relatively few plants had wilt symptoms at harvest, but 26.7% and 9.2% of the tubers harvested from plants infected with the race 1 and race 3 strains, respectively, carried latent infections. Some infected clones never yielded diseased tubers, however. The development of symptoms above ground was not correlated with the incidence of tuber infection in any particular clone. No tuber infection occurred in tolerant or resistant clones grown in infested soil at cool (12–22°C) temperatures. Tubers were inoculated directly in an attempt to evaluate the ability of bacteria to multiply in these tissues at different temperatures. Highly virulent strains ofP. solanacearum survived in susceptible tubers in higher numbers and for longer periods than in resistant ones. Low temperature (4°C) had a deleterious effect on survival of the bacterium in tubers, but did not completely eliminate the pathogen even after 40 days.     

Potential for improving freezing stress tolerance of wild potato germplasm by supplemental calcium fertilization

The main objective of the present study was to investigate the influence of supplemental calcium fertilization on the levels of freezing tolerance in different wild potato species. For this purpose, the freezing tolerance of a broad spectrum of theSolatium taxa was evaluated with and without supplemental calcium fertilization. Previous studies have shown that there is a large variation in the calcium accumulation capabilities among species and among various accessions within species. While this study confirms such variation, no direct relationship between the leaf calcium content and the improvement in freezing tolerance was found. Nevertheless, overall 45% of the species accessions had significant higher leaf calcium content and 52% of the species accessions showed a significant drop in the frost score average at the p<0.05 level. In terms of this experiment, a drop in the frost scores meant an improvement to withstand cold. One third of the frost tolerant accessions and 41% of the frost sensitive accessions showed both, a significant increase in leaf calcium content and at the same time a significant lower average frost score. The different response observed among the accessions may suggest that even though most of the accessions are able to accumulate calcium, only some of them may have the ability to benefit from the supplemental calcium. Future breeding schemes may be able to use this information for selecting clones that would respond positively to calcium fertilization in terms of frost survival. Results of this study also suggest that calcium fertilization may be used as a rather inexpensive cultural practice for protecting potatoes from frost damage. The results of the present study also suggest that soil calcium levels should be taken into consideration when freezing tolerance of potato germplasm is being evaluated.     

Tuber Resistance and Slow-Rotting Characteristics of Potato Clones Associated with the Solanaceae Coordinated Agricultural Project to the US-24 Clonal Lineage of <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Late blight, caused by Phytophthora infestans, is a devastating disease on potato worldwide and new lineages of the pathogen continue to develop in the U.S. Breeding for resistance is important for economic and environmental purposes. The Solanaceae Coordinated Agricultural Project (SolCAP) focuses on linking allelic variation in genes to valuable traits in elite cultivated potato germplasm. This research assessed the SolCAP diversity panel (206 clones in Washington and 213 clones in Wisconsin) for tuber resistance to the US-24 clonal lineage of P. infestans after potatoes were harvested from fields in Washington and Wisconsin in 2011. This is the first time this germplasm has been evaluated for tuber resistance to P. infestans using a non-intrusive zoospore inoculation technique. Clones with a percent incidence of 30% or less were considered resistant and only eight clones (Palisade Russet, AWN86514–2, MSL268-D, MSM171-A, MSM182–1, MSN230-1RY, Patagonia and Yukon Gem) were characterized as resistant at both locations. These clones have previously demonstrated high to moderate partial foliar resistance to isolates of P.infestans and therefore represent germplasm with both foliar and tuber resistance. Nine clones (AWN86514–2, F66041, MN 18747, MSM 182–1, MSN230-1RY, Modoc, Ama-Rosa, Patagonia and Purple Majesty), were characterized as slow-rotting at both locations with a mean percent internal rot of 75% or less after 33 days of storage. Two clones, MN 18747 and Modoc, are considered to have the highest risk of being a carrier for P. infestans of all the clones evaluated in the SolCAP collection. Not a single clone demonstrated complete tuber resistance to the US-24 strain at both locations.     

播种至苗期不同阶段冻害与持续时间对玉米幼苗建成及抗性生理的影响

以先玉335为供试品种，基于寒地典型玉米种植生态区的田间温度动态，采用两因素完全随机设计，分别设置冻害发生阶段和冻害持续时间处理，比较分析各处理组合条件下玉米幼苗形态建成及抗性生理指标的变化差异。研究表明，玉米播种至出苗各阶段发生冻害胁迫后，可不同程度延长玉米出苗时间、降低成苗率，甚至导致幼苗全部死亡。播后早期冻害通过降低种子贮藏物质转运效率，加剧膜脂过氧化，削弱叶片光能捕获能力等一系列不可逆影响，抑制幼苗形态建成，这些不利影响程度随冻害持续时间的延长而不断加强。播后冻害可诱导存活植株体内可溶性蛋白、脯氨酸、可溶性糖等渗透调节物质含量维持较高水平，以改善植株对低温环境的适应能力。玉米播种至出苗各阶段受冻害胁迫影响均较显著，且以播种10 d后植株对冻害最为敏感。     

Selection and utilization of solanum phureja clones with high resistance to different strains of pseudomonas solanacearum

Over 250 accessions ofSolanum phureja from Colombia and 300S. phureja—S. tuberosum hybrids were screened in the greenhouse for resistance toPseudomonas solanacearum (isolate K-60). Each plant was inoculated by stem puncture at the pre-bud stage and then held at a constant 28 C for 15 days. Seventeen clones with different levels of resistance to K-60 were inoculated with nine additional isolates representing all three races of the bacterium. The reactions of individual clones varied from resistance to almost all isolates, resistance to only one isolate, or complete susceptibility. Crosses amongS. phureja clones and betweenS. phureja and 24-chromosomeS. tuberosum stocks gave progeny with various percentages of resistant plants. Clones with resistance equal to that inS. phureja were found in theS. phureja × S. tuberosum crosses. Tests conducted in growth chambers showed that resistance was expressed more frequently at high light intensity (2000 ft-c) than at low intensities (1300 ft-c) at 24 C and 28 C. Resistance appears to be relatively simply inherited and the prospects for transferring a high level of resistance into cultivated forms are promising.     

Quality of potato tubers as affected by freezing: II. lipids and minerals

The effect of freezing on the chemical composition of Katahdin and Atlantic potatoes was studied. Tubers were exposed to a temperature of ?20°C for 24 hrs., then thawed for 1 hr. at 20°C prior to analysis. Frozenthawed tubers were compared with unfrozen controls for total lipid, phospholipid, fatty acid and mineral content. Following freezing, a significant (p<.01) decrease was observed in crude lipid and phospholipid content of both cortex and pith sections. Generally, an increase in palmitic acid and a decrease in linolenic acid occurred in the phospholipid fractions of both varieties. A decrease in both macro and micro mineral content also occurred following freezing.     

橡胶树低温伤害的生理反应

在人工零上低温下,巴西橡胶树(Hevea brasiliensis)叶质膜透性随低温处理时间的延长而持续上升,抗冷品系的上升速率比不抗冷品系慢。呼吸强度和ATP含量均随处理时间的延长而持续下降,抗冷品系下降速率比不抗冷品系慢。叶绿体Mg~(++)—ATPase活性也表现出明显抗性差异。可见,低温下叶组织的质膜透性、呼吸强度、ATP含量以及Mg~(++)—ATPase活性的变化与品系抗冷性有关。低温下呼吸强度、ATP含量与质膜透性变化呈负相关,质膜透性的变化与供能有关。     

Male fertility and freezing tolerance of hybrids involvingSolanum tuberosum haploids and diploidSolanum species

Summary Male sterility of (haploid x species) hybrids often hampers the exploitation of wildSolanum species in breeding for cold tolerance. In a study aimed at finding ways round these problems, we found that one accession of the cold tolerant wild speciesS. sanctae-rosae gave progenies segregating for male fertility in crosses withtuberosum haploids. Moreover, a source of male fertility restorer gene(s) was hypothesized in the (haploid x species) hybrid UP88-C80 (tbr x chc). A relatively high freezing tolerance was found in the progenies coming fromtuberosum haploid xsanctae-rosae crosses and some hybrids showed a freezing killing temperature as low as −5.4°C. Although the most tolerant clones did not shed pollen, at least one clone (Sr6,tbr x sct) combined male fertility, 2n pollen production and good freezing tolerance (−3.9°C) and might be directly used in crosses with tetraploidS. tuberosum in order to introgress resistance to low temperature intuberosum form. Contribution no. 137 from the Research Centre for Vegetable Breeding-CNR. Research supported by National Research Council of Italy, special project RAISA, subproject no. 2, paper no. 2776.     

Solanum commersonii cytoplasm does not improve freezing tolerance in substitution backcross hybrids with frost-sensitive potato species

Solanum commersonii Dun. (cmm) is the most frost hardy wild potato species known, being able to tolerate an acute freezing episode to about -5 C and further acclimate to tolerate ?10 C after being exposed to chilling temperatures for several days. Breeding with this species to incorporate its frost-hardiness traits can be accomplished by standard sexual hybridization or protoplast fusion. These methods can result in hybrids that vary in contribution of the cmm plastome. To test the effect of cmm cytoplasm, cytoplasmic substitution backcross hybrids were made with three very frost-sensitive species,S. brachistotrichum, S. cardiophyllum, andS. pinnatisectum, by usingS. commersonii as the female to make an F₁, then performing repeated backcross (BC) using the sensitive species as males. Relative freezing tolerance (RFT) of all genotypes was assessed by measurement of ion leakage of excised terminal leaflets subjected to a controlled ice nucleation and simulated freeze-thaw stress. Even against the background of these very sensitive species’ genomes, the cmm cytoplasm of substitution hybrids promoted insignificant improvement in frost hardiness or ability to acclimate. We conclude that either (1) cmm cytoplasm does not contribute to frost hardiness, or (2) if cmm cytoplasmic frost hardiness genes do exist, they must be epistatic to (depend on the presence of) nuclear hardiness genes for expression.     

茶园晚霜冻害及其防治

茶园晚霜冻害造成茶树芽叶焦灼甚至枝梢枯死亡,严重影响茶叶产量和品质。本文对晚霜冻害发生的原因及影响因素,就防御晚霜冻害发生的措施以及灾后补救等方面研究进行了综述,以期为有效降低晚霜冻害影响提供参考。