Resumo em português Objetivou-se, neste trabalho, estudar a conservação de pomelos (Citrus paradisi Macfad.) varieties 'Flame' e 'Henderson' revestidos com cera Sparcitrus e mantidos sob refrigeração (8º C ± 1º C e 95% ± 5% UR). Para cada variedade estudada, utilizou-se delineamento inteiramente casualizado, disposto em esquema fatorial 2 x 5, com 3 repetições, onde o primeiro fator correspondeu aos tratamentos com e sem a aplicação de cera (controle) e o segundo, ao tempo armaze (mais) namento (0, 10, 20, 30 e 40 dias). Cada parcela experimental foi composta por cinco frutos. Foram estudadas as seguintes variáveis: perda de massa, rendimento do suco, pH, sólidos solúveis (SS), acidez titulável (AT), SS/AT, açúcares redutores, açúcares não redutores, açúcares solúveis totais, vitamina C e aparência externa. A aplicação de cera é efetiva na preservação da aparência de pomelos 'Flame' e 'Henderson', não afetando sua qualidade interna. Resumo em inglês The goal of this work was to study the conservation of grapefruit (Citrus paradisi Macfad.) "Flame" and "Henderson" coated with Sparcitrus wax and kept under refrigeration (8º C ± 1º C and 95% ± 5% RH). For each variety studied, the experimental design was completely randomized, build up in factorial 2 x 5, with 3 replicates, where the first factor corresponded to the treatments with and without wax application (control) and the second factor to the storage period (0, (mais) 10, 20, 30 and 40 days). Each experimental parcel was composed of five fruits. The following variables were studied: mass loss, yield of juice, pH, soluble solids (SS), titratable acidity (TA), SS/AT, reducing, non-reducing and total soluble sugars, ascorbic acid and external appearance. Wax application is effective in the preservation of the appearance of grapefruits "Flame" and "Henderson", and does not affect their internal quality.
Resumo em inglês The writers review previous concepts concerning the reaction of citrus plants to the tristeza disease. It is recognized that environmental factors such as temperature, humidity and light can influence plant reaction, but these are considered of relatively minor importance. Characteristics of the plant itself govern its reaction to the disease and among those, resistance to infection, ability to permit virus increase and tolerance or non-tolerance of tissues are considered (mais) most important. Tests using viruliferous oriental citrus aphids for inoculation of various citrus types budded over sour orange rootstocks (table 1 and 2) showed a correlation between susceptibility to infection and severity of symptoms. The sweet oranges proved to be the most susceptible to infection and showed severe disease symptoms. The Barão sweet orange appeared to be more susceptible than Valencia. The mandarins tended to show some resistance to infection, but when infected, severe symptoms developed. The tolerant tangelos (7) behaved similarly to sweet oranges : They were very susceptible to infection and showed severe symptoms. The non-tolerant tangelos, susceptible citranges (7) and grapefruits behaved more or less alike, and showed medium susceptibility to infection and moderately severe disease symptoms. Among the grapefruits, Leonardy was. observed to be relatively more susceptible and showed more severe symptoms than Duncan. The pummelos, shaddocks and sour oranges were comparatively very resistant to infection and showed only moderate symptoms when infected. It has been found that the sour oranges can be more easily infected by tissue union than by the aphid vector. Poncirus trifoliata, citrumelos and resistant citranges showed no symptoms and no virus could be recovered from the inoculated plants even after three inoculations. The nature of injury caused by tristeza in the non-tolerant graft and intergraft combinations is discussed. The observation of symptoms shown by plants consisting of a sour orange inter-stem-graft between sweet orange roots and foliage seems to indicate that phloem collapse of the sour intergraft does not entirely prevent food translocation, since under field conditions the sweet stem below the sour intergraft continued, for almost two years, to increase in size at about the same rate as the sweet stem above. The growth of the sour intergraft was observed to be constricted and its lack of developments indicates a possible injurious effect of the disease on tissues other than the phloem. Root tissues of sour oranges have been found to be sensitive ;to injury, sincejsweet orange tops grafted directly onto sour orange roots and subsequently inoculated showed the usual tristeza symptoms. Death of rootlets and roots was found to occur not only in infected plants with tolerant tops and non-tolerant rootstocks but also on infected tolerant plants having an inter-stem-graft of non-tolerant sour orange. These observations and those made of root reaction on mechanically ringed plants indicate that although the root tissues of non-tolerant stocks may be sensitive to injury the rootlet and root symptoms are mostly secondary reactions. Tests carried out showed that the tristeza virus was recovered from insect protected sprouts grown at the ends of severed roots of Caipira sweet orange stock thus indicating that the virus was definitely present in the roots of a tolerant rootstock. Previously tristeza has been recognized as being associated with various citrus stock-scion combinations. In the present paper 50 seedling types have been reported as showing tristeza symptoms following heavy aphid inoculation. The symptoms shown by infected seedlings are similar to those shown by non-tolerant stock-scion combinations. Small sweet orange seedlings have been observed to show some symptoms of tristeza following heavy inoculations, but citrus types possessing tolerant tissues have shown a tendency toward recovery from symptom expression. The writers, on the basis of observed plant responses, have discussed the mode of inheritance of the main characteristis involved in plant reaction to tristeza. Some seedling progenies of known crosses between Poncirus trifoliata and sweet oranges (citranges) have been found to permit virus increase as the sweet orange parent does, whereas others behave like P. trifoliata and apparently do not permit virus multiplication. No relationship has been found between the trifoliata leaf-shape and inability to permit virus increase, since some of the hybrids that possess the trifoliata leaves, permit virus multiplication. Backcrosses of citranges to sweet oranges show a tendency to behave like the sweet orange parent. Hybrids between P. trifoliata and grapefruits (citrumelos) have behaved in most cases as the parent P. trifoliata. This seems to indicate that tolerant tissues and inability to permit virus increase are dependent on dominant factors in this type of cross. Hybrids between Citrus reticulata and C. paradisi (tangelos) do not show a clear-cut type of inheritance. Some tangelos behave Uke the mandarin parent, possessing tolerant tissues ; others behave like the grapefruit parent indicating possession of non-tolerant tissues. The inability to permit virus increase is a characteristic of little value in a rootstock improvement since tops of most commercial citrus varieties permit virus multiplication. It is pointed out that improvement of citrus rootstock with respect to tristeza should be aimed at combining tolerant tissues such as found in P. trifoliata or hybrids, C. sinensis, C. reticulata, etc., with other favorable characters such as vigor, resistance to gummosis, etc. Field tests showed that the reaction of infective buds on different rootstocks varies not only according to the tolerance of non-tolerance of the rootstock tissues, but also according to whether the buds themselves belong to types that possess non-tolerant or tolerant tissues. Infective buds of tolerant types, as sweet oranges, when budded on non-tolerant stocks produce a first flush of growth that is apparently healthy, but which later shows disease symptoms. For a period of about two months from date of budding, there is little or no difference between sprouts from healthy or infective buds of tolerant types. In contrast, when infective buds of non-tolerant types are budded on non-tolerant stocks, disease symptoms appear practically as soon as the buds start to grow. Observations indicate that infective buds from tolerant citrus types when budded on tolerant stocks usually do not develop symptoms even though the plant is a carrier of the virus. On the other hand observations indicate that infective buds of non-tolerant citrus types when budded on tolerant stocks may at times produce some symptoms. A possible explanation for the above-mentioned reactions is presented and is based on the relation between virus movement and food translocation in the plant. In the study of the relationship of tristeza virus to host tissues, plants composed of a sweet top over sour orange rootstock were allowed to develop two sweet orange branches. One branch of each plant was then ringed and inoculated by the vector. The branch not inoculated did not develop symptoms and 16 months after inoculation, buds were taken from the inoculated and the non-inoculated branches and tested for presence of virus. All buds taken from the inoculated ringed branches were found to be carrying the virus, whereas the buds taken from the other branch of the same plant did not have any virus. This experiment shows that the tristeza virus was not able to move across the ringed portion of the stem during that period, thus indicating that the tristeza virus is probably a phloem virus. Results from extensive buddings of various citrus stocks in the field indicate that buds taken from old sweet orange plants that have been known to be infected for a long time have been found to carry the virus in all buds. On the other hand, tests with buds taken from young plants recently infected, of Duncan grapefruit, sour orange and in some cases of Dancy tangerine and Valencia sweet orange, showed that not all buds were carrying the virus. It is not yet known whether buds that are mature prior to infection may temporarily escape virus invasion or whether citrus types which have non-tolerant tissues may limit to a certain extent complete systemic invasion of the tristeza virus.
Resumo em português Algumas regiões citrícolas, especialmente no continente europeu, ainda não foram, ao que parece, atingidas pela moléstia tristeza dos citros. Os conhecimentos adquiridos durante as investigações feitas sôbre a moléstia permitem indicar como identificá-la e prevenir suas desastrosas conseqüências nos laranjais. Os sintomas gerais nas plantas afetadas são semelhantes aos causados pela podridão do pé (gomose), podendo-se distinguí-la da tristeza examinando as (mais) raízes. Há combinações cavalo-enxêrto tolerantes e não tolerantes ao vírus. É, porisso, muito importante o reconhecimento da espécie cavalo, o que se pode fazer no pomar examinando a sua brotação ou observando o grau de congenialidade entre cavalo e enxerto. O teste colorimétrico feito com a casca da raiz também auxilia o reconhecimento. Os sintomas chamados "pitting" das limas ácidas e pomelos, permitem identificação da tristeza no pomar. O teste de Schneider, Wallace & Dimitan combinado com observações de campo, pode substituir, nas regiões onde a moléstia já foi constatada, os testes de transmissibilidade, mais rigorosos porém demorados, feitos no viveiro ou em estufas. A transmissão por enxertia ou por insetos vetores é feita da planta suspeita para plantas sadias de combinações não tolerantes ao vírus (laranjeira doce sobre azeda) ou para pés francos do limoeiro galego. É de interesse conhecer qual a estirpe do vírus predominante na região, para orientação dos citricultores quanto aos métodos de contrôle da moléstia. A identificação da espécie de afídios predominante na região permite prever a velocidade da disseminação da tristeza, porquanto umas são vetores muito eficientes, outras pouco. O contrôle da tristeza é obtido por métodos indiretos. Nas novas plantações evitam-se as combinações não tolerantes, empregando-se como variedade-cavalo as laranjeiras doces, as tangerineiras, os limoeiros Cravo (Rangpur) e Rugoso. Ãs vezes é possível o emprego de pés francos provenientes dos embriões nucelares. Nas plantações já existentes pode-se fazer a substituição total ou parcelada (individual) das plantas, conforme se constate predominância de afídios muito ou pouco eficientes e de estirpes fortes ou fracas do vírus. A sub-enxertia ("inarching"), a sôbre-enxertia ("topworking") e o afrancamento do enxerto são outras tantas modalidades de controle da tristeza, as quais podem ser vantajosamente empregadas em determinadas condições. Medidas de quarentena podem retardar a invasão das zonas ainda livres da tristeza, -sendo de interesse o esclarecimento do público quanto ao perigo representado pela importação de plantas ou suas partes vivas, exceto as sementes. Resumo em inglês The tristeza disease of citrus has not yet been reported from European countries nor from various other citrus growing areas of the world. Investigations on the disease have been carried out in various countries, such as Argentina, Australia, Brazil, South Africa, and United States. Knowledge obtained from these investigations enables citrus experts from areas not invaded by tristeza to recognize its presence in the orchards and to prevent disastrous losses for the indust (mais) ry. General decline symptoms of tristeza resemble those caused by foot rot, but root examination permits the differentiation of the two diseases. Presence of pitting symptoms in trees of West Indian limes or of grapefruits permits easy diagnosis of tristeza in the orchards. Stock-scion combinations may be tolerant or intolerant to tristeza. Thus, it be comes important to determine the rootstock in case of plants showing decline symptoms. This fact can be established by direct examination of sprouts from the rootstock or by observing the degree of congeniality of rootstock and scion. The colorimetric tests made with bark of the rootstock may help to determine it. Field observation of symptoms complemented by Schneider's histological tests may replace the transmission tests for field surveys of the disease in areas where tristeza is already known to be present. Transmission tests are usually carried out by methods of tissue union or by means of the vectors. Young plants of non-tolerant combinations (such as sweet orange on sour orange rootstock) or seedlings of West Indian limes may be used as test plants in these tests. A knowledge of the predominance of the various strains of the tristeza virus complex in the invaded areas is very important in regard to the application of control measures. Also the determination of the aphid vector or vectors in the areas concerned will permit forecasting the rate of spread of tristeza because efficiency varies considerably according to the vector species. Control of tristeza in citrus orchards is obtained by indirect methods. In new plantings made in invaded areas, non-tolerant stock-scion combinations should be avoided. Only tolerant rootstocks such as sweet oranges, mandarins, rangpur lime, and rough lemons should be used for most commercial tops. In some instances it may be possible to use unbudded trees originated from nucellar embryos. In established orchards, where a non-tolerant rootstock was employed, individual affected trees may be replaced or the whole planting may be interplanted with trees of a tolerant stock-scion combination. The first method is used in areas where the disease is disseminated by a poor vector, whereas the second method is more advisable in areas where spread of the disease is very rapid. Inarching or rooting the scion (by mounding the soil around its base) are used to control tristeza under some conditions. Top working with lemon may also be used. Quarantine barriers may prevent the introduction of tristeza in uninvaded areas. It is highly desirable to inform travellers about the risk represented by the introduction of citrus budwood material or cuttings from areas where the disease is known to be present.
Resumo em português Mudinhas novas de laranjeira azêda podem ser infetadas com o vírus da tristeza por meio do afídio vetor da moléstia ou mais fàcilmente por enxertia. Plantas adultas são muitos resistentes, quase imunes. A recuperação do vírus da tristeza de plantas de laranja azeda infetadas é efetuada com facilidade por meio de enxertia e com muita dificuldade por meio do vetor. Os sintomas comumente apresentados por mudinhas de laranja azêda afetadas, consistem em amarelecime (mais) nto das fôlhas novas, paralisação no crescimento e eventual queda das fôlhas amareladas. Em caso de infecção com estirpes fracas do vírus, os sintomas são menos evidentes e comumente há recuperação. As fôlhas formadas após recuperação, muitas vêzes apresentam palidez de pequenas extensões das nervuras. Os tecidos do floema da laranjeira azêda, abaixo do enxêrto de laranjeira doce infetada, mostram degeneração. Êstes sintomas têm sido utilizados para distinguir a tristeza de outras moléstias que causam declínio da planta. Sintomas de depressões no lenho ("pitting") raramente se manifestam em laranjeira azêda. Não se conhece presentemente nenhuma variedade de laranja azêda tolerante à tristeza, não se podendo, portanto, utilizar êsse cavalo para copas nas quais o vírus da tristeza se multiplica e atinge concentrações elevadas. Entretanto, a laranjeira azeda ainda pode ser usada como cavalo para alguns limões dos tipos Eureka e Siciliano e para a própria laranjeira azêda, em áreas invadidas pela moléstia. Há possibilidade de que o cavalo de azêda possa vir a ser novamente empregado para variedades que usualmente perecem quando nela enxertadas, lançando-se mão de medidas auxiliares como a inoculação prévia da copa com uma estirpe fraca do vírus, pela utilização do tipo de copa com união múltipla, etc. Borbulhas de plantas de laranja azêda afetadas pela tristeza nem sempre encerram o vírus. Borbulhas de plantas afetadas ou de plantas sadias se desenvolvem mais ou menos satisfatòriamente quando sôbre-enxertadas em galhos de laranjeira doce sobre laranjeira azêda, já em avançado estado de declínio. Uma copa mista de laranjeiras azêda e doce sôbre cavalo de azêda pode causar alguns benefícios à planta afetada pela tristeza sob determinadas condições, mas êsse benefício não é duradouro e o método não oferece possibilidades práticas. A laranjeira azêda em viveiro tem sido utilizada com vantagem na determinação da presença do vírus da tristeza em borbulhas de vários tipos de Citrus, pela observação do crescimento feito a partir dessas borbulhas em comparação com aquêle de borbulhas da mesma variedade garantidamente sadias. Para a determinação da presença de estirpes fracas do vírus o método é mais demorado. Interenxertos de laranjeira azêda entre copas e raízes de laranjeira doce são suficientes para que haja manifestação de sintomas da moléstia. Há aparentemente alguma translocação através do interenxêrto, pois o desenvolvimento do cavalo abaixo e acima dele é aproximadamente igual. Resumo em inglês Young sour orange seedlings are more easily infected with the tristeza virus by approach-grafts than by means of the aphid vector. Under natural conditions adult plants in the field are highly resistant to infection by the aphid vector. Recovery of the tristeza virus from infected sour orange plants is also more easily accomplished by tissue union than by means of the aphid vector. Sour orange seedlings show yellowing of young leaves followed by stunting and shedding of l (mais) eaves when infected with the ordinary strain of the tristeza virus in Brazil. These symptoms do not differ from those described for seedling yellows. The symptoms of leaf yellowing are less evident in plants infected with mild strains of the tristeza virus and there is subsequent recovery. New flushes of young leaves may show occasional vein dashes. Sour orange tissues below the bud union of the sweet orange onsour orange rootstock show phloem degeneration when the plant is affected with tristeza. These degeneration symptoms have been used to distinguish tristeza disease from other decline diseases that affect the same stock-scion combination. Over 45 varieties of sour oranges have been tried as rootstocks for tristeza infected sweet orange tops and they all behaved as non-tolerant rootstocks. So far no tristeza tolerant sour orange rootstock is known, but it seems entirely possible that crosses between sour orange and tristeza-tolerant citrus varieties may yield F1 hydrids that combine the desirable characteristics of the sour orange rootstock with tristeza tolerant tissues. In case such an F1 hybrid produced large number of nucellar seedlings these could be used as rootstocks. Sour orange varieties can be used as rootstocks for commercial acid lemons or sour orange tops even in areas where tristeza is present. There is as slight possibility that if a somewhat tolerant sour orange is found, it might be used a3 rootstock for grapefruits, sweet orange, mandarin, and other tristeza susceptible tops if complementary controlling measures are employed such as protective inoculation of the scion with mild strains of the virus, use of multiple bud union, etc. Tests have shown that buds from a single budstick taken from a tristeza infected sour orange plant may produce healthy and diseased tops when budded on a sour orange rootstock, thus indicating that tristeza virus was not present in all buds of the infected plant. It has been observed that commercial acid lemon and sour orange buds make satisfactory growth when top worked on tristeza-diseased sweet orange tops on sour orange rootstocks. Attempts have been made to control tristeza disease in sweet orange on sour orange rootstock by inducing the rootstock to develop sprouts and thus produce a sour orange top that would supply sinthates for the roots. The presence of this composite sweet orange and sour orange top may be of benefit to the plant when it is infected by tristeza, but this effect is not lasting and the method has been unsuccessful when tried in commercial orchards in Brazil. Sour orange seedlings in nursery rows have been used in Brazil to determine the presence of the ordinary strains of the tristeza virus in budwood from many citrus varieties. In this "sour test" the growth of buds to be tested has been compared with the growth of healthy buds of the same variety. Intergrafts of sour orange stem between a sweet orange top and a sweet orange rootstock were sufficient to induce the plants to show tristeza symptoms when infected. Three, 10, and 80-100 cm intergrafts were tried and even the 3 cm intergraft was enough to cause injury in the infected plants. When sweet orange was budded with a multiple union, i. e. on three or four upper branches of sour orange plants there was less apparent injury from tristeza virus infection than in case of a single bud union.
Resumo em inglês 1 - The present paper deals with the results of studies on pollen fertility, number of seeds per fruit and frequency of polyembryony in Citrus. 2 - The pollen may be divided into four groups of which the first consists of the living and functional grains, colouring deeply with carmín acetic, germinating in sugar solutions fairly well. The remainny three types : half filled grains, empty grains, and small deformed grains are all inviable. 3 - The grains are generally sphe (mais) rical, 15 to 40ix in diameter. The smallest grains were found in Citrus hystrix and Citrus mitis (fig. 3 and 4), while citron and the grape-fruits have the largest grains (fig. 1, 2 and 5). 4 - Size and form are reasonably constant, except the hybrid "Citran-gequat", "limão galego" without spines, orange "Ruby" (fig. 6 to 8). 5 - Percentages of viable pollen grains are given in quadros IV to X. Tahiti Lime, probably a triploid, is completely sterile. "Baía" orange (Washington Navel orange) is completely male sterile, while the fruits of it may have some seeds. The two seedless varieties of "lima" and "pera" have 37,1 and 9,3% of viable pollen respectively. Regarding pollen viability oranges are the most variable. They show from 0 to 90% of good pollen (quadros IV and V). In lemons and limes the percentages vary from 50% and 80% (quadros VI to VIII). Tangerines, with exception of Satsuma owari, have generally more than 60% of good pollen. The grape-fruits, except the case of "Marsh-seedless", are characterized by a relative high pollen fertility. 6 - There is a certain variation of pollen fertility due to the external conditions. It seems to exist also a certain effect of the rootstock, on viability of pollen grains, as shown for the rootstock of "sour orange" and "rough lemon". 7 - The number of seeds per fruit was also determined and is given in the respective quadros (IV-X). 8 - There does not exist any consistent difference between open pollinated and selfed flowers in regard to the number of seeds per fruit (quadro XII). In 26 cross pollinations (quadro XIII), 6 caused an increase, 11 a decrease in the number of seeds. Especially interesting in this respect was "Baía" orange (Washington Navel), where, for instance, the cross pollination with the orange "Barão" gave in average 7 seeds per fruit, while in the cross with "Hamlim" the seed number was only 2,75 per fruit, this difference being highly significant. 9 - It is a well known fact that nucellar embryony is quite common in Citrus. The frequency of polyembryony has been determined for a large number of types. Even if an embryo is formed, we may not be certain whether it is produced by an adventicious growth of the nucellus or from a normally fertilized egg, as shown for instance for Citrus mitis x Poncirus trifoliata. (Fig. 15 and 16). Both twin embryos may be apogamous or one only, the other being in this case an hybrid. 10 - There exists a slight positive correlation between number of seeds and percentage of good pollen, with r = -f- 0,53. It should not be forgotten that the individual variations for these characters are very high, with coefficients of 93,01% for seed number and 33,18% for the percentage of viable pollen grains. Furthermore the variation of the forms is decidedly asymetrical owing to the pressure of the 0 limit. The general situation is best illustrated by the graph 1. With 0 to 10 seeds per fruit, there is no ordely variation of the percentage of good pollen. If the number of seeds rises between 10 and 20 seeds, the percentage of viable pollen grains rises generally above 50%, and if the number of seeds is still higher, the percentage surpasses 70%.