Occurrence and meteorological factors of corn rust disease and yield losses

玉米銹病在本省有普通型（由Puccinia sorghi引起）及南方型（由P. polysora引起）兩種。然而，目前以南方型銹病發生較為普遍。銹病病勢進展一般呈開口向下之二次方曲線，但發病較重時則呈一次方直線。銹病的發生和氣象因子有關，春作玉米南方型誘病的發生和發病7天前之溫度24.1~28.0℃及28.1~32.0℃相關最大，秋作玉米則和8~14天前之溫度20.1~24.0℃、24.1~28.0℃及28.1~32.0℃相關最大。利用複迴歸分析鎊病病斑面積率及侵染速率和氣象因子之關係可得到迴歸方程式，將不同年代、不同期作之氣象因子代入方程式時可得到預測值，經比較預測值與實測值甚為接近，可做為預測之用。 在產量損失方面，本省尚缺有關研究報告。在國外，Russell 1965年報告，普通型銹病利用6個雜交組合經過兩年的結果，其產量損失在15.3~23.5％。Kim及Brew-baker 1976年報告普通型銹病對產量及農藝性狀之影響，在子實產量有35％之減產，在鮮草重有27％之損失，在穗長有11％之差異，在穗徑有10％之不同，在株高、穗位高及吐絲期有5%之差別。Randle等1984年利用兩個甜玉米品系Jubilee（中感）及StylePak（感）觀察其農藝性狀之差異，結果顯示在銹病發生區及無銹病區在吐絲期，穗長、穗徑及果穗含水率均有明顯的差異。Pataky1987年利用甜玉米品系Gold Cup（中抗）、Stylepak（感）及Florida Staysweet（感）來比較普通型銹病引起之產量損失，結果顯示收穫前一週調查時每10％銹病引起6%穗重及6.5％穗數之損失。在南方型銹病方面，Rodriguez-Ardon等1980年報告利用感病雜交品系在1976及1978從5月25日開始每隔兩週種植一次，共種三次，其予實產量減產4、23及45%，所以晚植者產量損失特別高。 Two kinds of corn rust, common rust (Puccmia sorghi) and southern rust (P. polysora) were found in Taiwan, However, southern rust is more wide-spread at present. Disease development of corn rust showed quadratic regression curve equations in general, but it showed linear equations when the disease was serious. By analyzing the single correlation of rust and meteerolgical factors, it indicated that the most important factors were temperature 24.1~28.0℃ and 28.1~32.0℃ seven days before disease occurrence during spring crop, and 20.1~24.0℃、24.1~28.0℃、28.1~32.0℃ 8~14 days before disease occurrence during fall crop. By analyzing the relationship between increasing infected leaf area percentage and meteorological factors, 8 equations were obtained, while 11 equations were obtained from the relationship between infection rate and meteorological factors Those equations were derived from fall crop of 1990 at Chia-yi area. The predicted values from those equations obtained were very close to the obsened values, therefore, it is suggested that those equations might be used for predicting rust disease of corn. For yield losses caused by rust disease, not much information was found in Taiwan. Russell in 1965 reported that the losses on grain yields caused by common rust were 15.3?3.5% after 2 years tests on 6 crosses. Kim and Brew- baker in 1976 indicated that the effects of common rust on grain yield was 35%, fresh plant weight with ear was 27%, ear length was 11%, 10% on ear diameter, and 5% difference on plant height, car height, and silking stage. Randle et a in 1984 by using two sweet corn lines Jubilee (moderate susceptible) and Stylepak (susceptible) to observe the differnces on agronomic characteristics, the results showed that the silking stage, ear length, ear diameter and ear water content were quite different on rusted and non-rusted plots. Pataky in 1987 estimated that yield reduction due to common rust on Gold Cup (moderate resistant), Stylepak (susceptible) and Florida Staysweet (susceptible) was 6% of the maximum total ear weight and 6.596 of the maximum total number of marketable ears for each 11)36 rust severity. Roe driguez-Ardon et al showed that on susceptible hybrids, in three biweekly plantings (beginning about 25 May) in 1976 and 1978, southern rust caused average yield reductions of 4、23 and 45% respectively

LEAF BLIGHT OF TRAPA TAIWANENSIS NAKAI CAUSED BY RHIZOCTONIA SOLANI KÜHN

Leaf blight disease on Trapa taiwanesis Nakai leaves were collected from Singhara-nut growing areas in southern Taiwan. The symptoms on the leave first appeared as small, round watersoaked spots or irregular brownish-black spots. Water-soaked or irregular brownis-black spots gradually enlarged and coalesced with others, and finally the leaves were partially or entirely rotted. Sclerotia were formed on or near the diseased. In addition to leaves, the disease also damaged the petioles and stems of the plants. From the symptoms, morpholgy of the pathogen and inoculation tets, we concluded that Trap a taiwanensis Nakai was a new host of Rhizoctonia solai Kühn

Ecology and control of downy mildew on cucurbits

瓜類露菌病係由Pseudoperonospora cubensis所引起，在本省胡瓜、洋香瓜、哈蜜瓜及絲瓜等瓜類發生普遍而且嚴重。胡瓜或洋香瓜之摘葉，在15、20及25℃下接種後4~5天可形成病斑，在15及20℃下經5~6天，25℃下經6~8天可產胞，但在10、30及35℃不產生病斑，亦不產胞。病原菌胞子囊發芽以10及15℃最合適，6小時後發芽率達95.18%及97.52%，高溫發芽率降低。胞子囊釋放游走子之數目以7個最多，3及11個最少。胞子囊在2%水瓊脂上於30℃一天後再放回15℃，需經4小時始可發芽，發芽率為20.87%，24小時發芽率達63.11％。若在35℃一天後再放回15℃，則需經24小時始可發芽，發芽率僅7.01%，48小時後發芽率僅22.42％。若將病葉放在30℃一天後，再放回15℃，則其上之胞子囊需經4小時始可發芽，病葉放在35℃一天後，再放回15℃，則其上之胞子囊需經24小時始可發芽。胞子囊之發芽率隨相對濕度之增加而增加，在相對濕度55、81、95及100%時，其發芽率分別為29.85、66.30、80.02及97.53%。在水瓊脂培養基中瓊脂之含量亦影響胞子囊之發芽率，瓊脂含量2.0時發芽率在15℃24小時後高達99.30%，瓊脂含量3.0％時發芽率亦達96.91%，但含量至8.0%時則胞子囊不發芽。胞子囊在V-8汁濃度越高，發芽率越低，濃度達35%時胞子囊不發芽。胞子囊在土壤含水量功％，經24小時尚不發芽，4天後發芽率僅2.66%，其發芽率隨含水量之增加而增加，50％含水量時24小時後之發芽率為20.38%。胞子囊在30％含水量土壤中至少可存活14天。胞子囊製成胞子懸浮液後在15℃經6及24小時接種，植株均可發病，但存放48小時者不發病。 分析胡瓜罹病度增加和氣象因子之關係，顯示露菌病和發病前7天及8~14天之降雨量呈正相關，但和平均相對濕度呈負相關。 在藥劑篩選，洋香瓜播種後三週之植株(1)先行噴藥一天後，再接種胞子懸浮液(4×10 4/ml)，經10天後調查葉片發病等級，再換算被害度(2)先接種胞子懸浮液後，約五天後開始發病時再施藥，經10天後調查發病葉片之等級，再換算被害度。結果以先噴藥再接種者，其被害度較先接種再噴藥者為低，藥效以58%鋅錳滅達樂可濕性粉劑及75%四氯異苯腈可濕性粉劑500倍效果最佳。 Cucumber downy mildew caused by Pseudoperonospora cubensis was quite Wide-spread and serious on cucumber, melon, muskmelon and loaf in Taiwan. The lesion formed at 4-5 days after inoculation on detached leaves of cucumber and melon under 15, 20 and 25℃. Sporulation at 5-6 days under 15 and 20℃, 6-8 days under 25℃. No lesion formation or sporulation under 10, 30 and 35℃. The optimal temperatures for sporangial germination were observed at 10℃ and 15℃ after 6 hours of incubation, the percentage of germination were 95.18% and 97.52%, respectively. Germination decreased at higher temperature. Most sporangia produced seven zoospores with an average of 6.7, a few sporangia produced 3 or 11 zoospores. The sporangia of Pseudoperonospora cubensis were incubated at 30℃ for one day, and then transferred to 15℃ , additional four hours were necessary to germinate, the germination percentage was 20.87%. As long as at 15℃ for 24 hrs the germination percentage increased to 63.11%. If the sporangia were incubated at 35℃ for one day first arid then transferred to 15℃, another 24 hrs were needed for germination, and the germination percentage was only 7.01%. Even at 15℃ for 48 hrs, the germination percentage was also increased to 22.42% only. If the infected leaves with sporangia were incubated at 30℃ for one day then moved to 15℃, the sporangia also took 4 hrs for germination. While the infected leaves with sporangia were incubated at 35℃, it required 24 hrs for germination. On the other hand, the germinability increased with increasing relative humidity, at the RH of 55,81, 95 and 100% the germination percentage were 29.85, 66.30, 89.02 and 97.53%, respectively. The percentage of germination of sporangium was influenced by agar concentration of water agar medium. When the agar contents were at 2.0% and 3.0% the germination percentage were 99.30 and 96.9%, respectively, after 24 hrs of incubation at 15℃. As agarcontent reached 8.0%, no germination was observed. Sporangia did not germinate on the leaf juice of Cucurnis melo. When the sporangia were incubated on V-8 juice, it showed that the higher the concentration of V-8 juice, the lower the germinability was observed, arid 35% of V-8 juice inhibited, germination. In soil with 30% water content the sporangia did not germinate even after 24 hrs of incubation. After 4 days of incubation, the germination percentage was only 2.66%. Therefore, the germinability increased with increasing water content. The sporangia could survive at least 14 days under 30% of water content in the soil. The downy mildew fungus of cucurbits maintained its infectivity in spore suspension after 6 of 24 hrs preparation, however, after 48 hrs, no infectivity was observed. The relationship of disease severity increment was meteorological factors was analyzed. Which indicated that downy mildew disease was positively correlated with rainfall at 7 and 8-14 days before disease occurrence; but negatively correlated with average relative humidity. Fungicide trials showed that the disease rating was lower on the plot which the seedlings were treated with fungicides first and then inoculation was made. Among the fungicides tested, 58% Metalafyl + Mancozeb wp and 75% Chiorothalonil wp showed the best effectiveness

Studies on the relationship of disease severity of yield and yield loss of rice sheath blight disease

水稻臺南5號及臺中在來1號因紋枯病為害之產量及產量捐失分為發病程度A.B.C及D四級，A為接種後不施藥，使病斑達到劍葉，B為接種後病斑選第四葉鞘（由下向上算）時，即以殺菌幫噴射，C為接後病斑達第二葉鞘時，即以殺菌劑噴射，D為對照區，不接種，且以殺菌劑噴射。臺南5號在第一期作A.B.C及D處理下，其產量每公頃各4000.0, 5466.7, 6433.3及7033.3公斤，其相對損失為43.0, 22.3, 9.0及0%，第二期作A.B.C及D處理下，其產量每公頃各為3866.7, 4746.7, 5093.3及5680.0公斤，其相對損失為31.9, 16.3, 10.1及0%。臺中在來1號在第一期作A.B.C及D處理下，其產量各為4400.0, 4500.0, 6033.3及6566.7公斤，其相對損失為32.9, 27.5, 8.5及0%，第二期作A.B.C及D處理下，其產量每公頃各為5111.1, 6153.8, 6478.6及6931.6公斤，相對損失為26.2, 11.3, 6.6及0%。臺南5號之被害度與產量之相關關係，第一期作Y=6984.54-33.46X (r=-0.9967),第二期作Y=5751.93-21.28X (r=-0.9943)，臺中在來1號之被害度與產量之相關關係，第一期作Y=7001.33-25.39X (r=-0.9538)，第二期作為Y=7030.18-19.39X (r=-0.9 916)

Prediction of Rice Leaf Blast. I. Meteorological Variables and the Development of the Number of Lesions

利用逐步迥歸法分析氣象變數與水稻臺南五號及臺農六十七號葉稻熱病之關係，建立十三個預測方程式，以預測葉稻熱病S型病斑數目之進展。當不同年度之氣象變數及發病資料綜合分析時所得之預測方程式，其預測值與實測值比各年度之個別資料分析時所得之預測方程式更為接近。 綜合分析由第一組氣象變數所得之預測方程式所包含之變數有最低氣溫、平均氣溫、氣溫在21~24℃之小時數，最高相對濕度、相對濕度90%以上之小時數及雨量等六個變數，而由第二組氣象變數所得之預測方程式所包含之變數有氣溫在18.1~21℃之小時數，24.1~27.0℃之小時數，相對濕度75.1～85.0%之小時數，90.1~95.0%之小時數及降雨量等五個變數。個別分析第一組氣象變數所得之預測方程式所包含之變數有最低氣溫、氣溫在21~24℃之小時數及最高相對濕度等三個變數，而由第二組氣象變數所得之預測方程式所包含之變數有氣溫15.1~18.0℃之小時數，相對濕度75.1~85.0％之小時數，相對濕度85.1~90.0%之小時數及露水時間等四個變歡，不同之預測方程式包．含3~4個不同之氣象變數。 預測方程式之R2（決定係數）均達極顯著，同時其平均變異值除有二個方程式在預測1977及1978年時高於10％以外，其餘變異值均在10%以下，故所得之預測方程式具有準確性。 A stepwise regression was used to analysis the relationships between meteorological variables and blast incidence of rice cultivars, Tainan 5 and Tainung 67. Thirteen predicting cquations were obtained for predictir.g the development of the number of “S” lesions. When data from various years were combined for analysis, the equations obtained were more agreeable between measured and estimated values than equations derived from those of individual years. The most important independent variables included in the predicting equations derived from the first group of meteorological variables combined together for analysis, were minimum temperature, average temperature, hours of temperature 21-24℃, maximum RI-I, hours of RH over 90%, and quar.tity of rainfall. The independent variables in the equations derived from the second group of meteorological variables, were hours of temperature 18.1-21.0℃ and 24.1-27.0℃, hours of RH 75.1-85.0% and 90.1-95.0%, and quantity of rainfall. When the meteorological variables were analyzed separately, the independent variables included in the equations from the first group of meteorological variables, were minimum temperature, hours of temperature 21-24℃, and maximum RH. The independent variables from the second group of meteorological variables, were hours of temperature 15.1-18.0℃, hours of RH 75.1-85.0% and 85.1-90.0%, and dew period. Each predicting equations contained 3 to 4 various meteorological variables. Coefficients of determination (R2) in the predicting equations were significant at 1% level, and the average variations of all the equations, were under 10% except two of them showing higher than 10% in 1977 and 1978. Therefore, it was thought that the equations were reliable for predicting the development of “S” lesions of rice leaf blast

SCLEROTIUM ROT OF TRAPA TAIWANENSIS NAKAI IN TAIWAN

Scierotium rot of Trapa Taiwadensis Nakai was found on September, 1980 in several Singhara-nut growing regions in southern Taiwan. Symptoms on the leaves first appeared as small, round, discolored and water-soaked spots. The spots gradually enlarged and coalesced with others to form large, irregular soft rot tissues. Dense mycelium and abundant sclerotia were produced on both surfaces of the leaves shortly after infection. The disease not only caused serious damage to the leaves, but also attacked the petioles and stems of the plants. From the symptoms, morphology of the pathogen and inoculation tests, it showed that this disease was caused by Scierotium rolfsii Saccardo. This is a new record of plant disease in Taiwan

Prediction of Rice Leaf Blast. III. Meteorological Variables and Percentage of Leaf Area Infected by Pyricularia oryzae

利用復迴歸分析1979~1984年臺農67號之病斑面積率與氣象變數之間的關係，建立六個方程式來預測稻熱病在發病最高峰期之病斑面積率，並以1985年之氣象變數與病斑面積率數據來驗證此等預測方程式之準確性，結果顯示其各預測值與實測值之數據甚為接近，且依病斑面積率與產量損失之關係，預測值與實測值屬於同一級數。各預測方程式係以病斑面積率與其角度值為因變數分別求得的。分析的結果，顯示轉角與否並無顯著的差別。在所建立的預測方程式含有3~4個氣象變數，分別為平均相對濕度，相對濕度在90％以上之小時數，降雨量及降雨日數，預測方程式中R2之值為0.89~0.96。在六個預測方程式中，四個係由二月中旬的之氣象變數組成的，而其餘二個係由二月下旬之氣象變數組成的。 By using multiple regression to analyze the relationships between meteorological variables and percentage of leaf area infected by Pyricularia oryzae on rice cultivar, Tainung 67, six reliable predicting equations were derived. The equations derived from 1979-1984 were tested in 1985. The results shoved that the predicting values were close to the observed values. The predicting equations were obtained by using percentage of diseased leaf area with and without arcsin transformation. Equations derived from transformed and untransformed data were similar. The equations contained 3-4 meteorological variables, such as average RH, hours of RH over 90%, rainfall and rainy days. The coefficients of determination of the equations were 0.89-0.96. Among the six equations, four were derived from the meteorological variables of middle February, and the other two were derived from late February

(19(1):57-63)木瓜腰折病之研究

Among the varieties of papaya plants to damping-off indicated that the variety of “Line 1” Solo is the most susceptible to this disease, the percentage of its infestation reached about 26.6%. Some new varieties of papaya plants introduced were Costa Rica and A4 (H. P.) which have been proven to be the most resistant to this disease. The percentage of its infestation ranged from 2.3 to 4.7% in these varieties. Up to now, the “Solo 1” variety is widely cultivated in southern Taiwan. The damage of this variety frequently causes heavily injury under favorable conditions. The damping-off is rapidly developed in the seedling stage, particularly in raining season, because the weather frequently changes high humidity at fine days and the temperature is constantly very high. However, the disease is chiefly affected by rainy days and temperature. The fungi were isolated from the diseased tissues of various papaya in the seedbeds and orchards, when five kinds of fungi have been found to be Fusarium spp., Rhizopus spp., Rhizoctionia sp., Phytophthora spp., and Pythium sp., among which the Fusarium spp., and the Rhizoctonia sp. are more important than other ones. 在所觀察的木瓜品種中，以蘇魯1號最易感病，其發病率達26.6％，一些引進品種以Costa Rica及A4 (H. P.) 最抗病，其發病率為2.3及4.7％。 目前蘇魯1號為臺灣南部栽培最廣的品種，但在高溫、高濕的雨季，常遭致腰折病為害。由試驗結果得知，本病與高溫，下雨日數及雨量有密切關係。 從病組織分離得的病原菌，以Fusarium spp.最多，其次為Rhizopus spp.及Rhizoctonia sp. Phytophthora spp.及Pythium sp.最少，由另一試驗得知，Rhixoctonia sp.為木瓜腰折病一種重要的病原菌