DIE INVLOED VAN RADIALE HARSGEïNFILTREERDE KERNSKEURE OP DIE GESAAGDE OPBRENGS UIT PINUS ELLIOTTII ENGELM.-SAAGBLOKKE / THE EFFECT OF RADIAL RESIN-INFILTRATED SPLITS ON THE YIELD OF SAWN TIMBER FROM PINUS ELLIOTTII ENGELM. SAWLOGS

A number of complaints, regarding the presence of resin-infiltrated splits in seasoned boards produced from Pinus elliottii sawlogs supplied from certain stands in State Forests, led to an investigation to determine the incidence of the defect and to find possible causes.

This paper deals mainly with the study of the first aspect. In the investigation two samples of stems were selected by a semi-random method from one mature stand, being clearfelled, in Entabeni State Forest (Northern Transvaal) and from three stands receiving, or due to receive, their fifth thinning. The clearfelling and thinning had produced logs containing heart shakes and this had given rise to the complaints.

During log preparation it was attempted to prepare as much as possible of the stem length into the longest sawlogs, working as closely as possible to the maximum limits for sweep and knots allowed by the departmental log specifications. This attempt resulted in the preparation of some logs containing slightly more than the permissible defects. Observations were made on stump surfaces of the orientation of shakes, and on log ends of their occurrence higher up in the stem, in an attempt to find a link between shake orientation and the known direction of strong winds, and to determine the height in the stem to which shakes extended from the stump. The orientation study produced no definite proof that wind was responsible, although there were strong indications.

This was followed by sowings up the logs mainly into structural timber, kiln seasoning and grading in two ways, viz A ignoring the resin-infiltrated checks and splits but taking all other defects pertinent to the relevant grades into consideration, and B taking all defects, including the checks and splits into consideration (Table 4). During the grading further measurements were taken on boards containing splits, to determine to what heights in the stem the shakes extended.

From the grading results, total and graded yields of sawn timber were computed, the differences in yields between the two grading procedures being a measure of the incidence and seriousness of the shake defect. Within log classes, (see footnote to Table 2) the yields obtained separately for each 2 cm top U.B. diameter class into which the logs had been segregated prior to sawing, were weighted according to the percentage size distributions of the logs yielded by the clearfelling and thinning operations in the relevant compartments, to obtain a weighted average for the log class.

The heights to which shakes were present in the stems of the two samples are shown in Table 3(a) while their incidence in logs of the various size classes are shown in Table 3(b). It is seen that shakes were more frequent and serious in the larger logs.

The presence of shake in the log samples, taken as a whole, caused only minimal yield losses (Table 4) but had the effect of somewhat reducing average board length (Table 5). However, sawn and graded yields are still excellent and the species should not be discriminated against in afforestation, because of the sporadic occurrence of the defect.

The yield figures should be of some value to sawmillers processing both normal and shake-containing logs of this species.     

Molecular characterization of avipoxviruses circulating in Windhoek district,Namibia 2021

Samples from eleven birds (chicken, dove and peacock) with symptoms of fowlpox, caused by the avipoxvirus (APV), were collected in seven different areas of the Windhoek district, Namibia between April and October 2021. A fragment of the 4b core protein and the DNA polymerase gene of APV were amplified by PCR from the DNA of the samples and sequenced. Phylogenetic analysis revealed that the viruses present in the chickens all belonged to clade A1 while the viruses in the doves and peacock were from subclade A3.1. This is the first report of subclade A3.1 avipoxvirus in peacock. In addition, all of the samples obtained from chickens were shown by PCR to be positive for the integration of reticuloendotheliosis virus while those from the doves and peacocks were negative. This study is the first characterization of avipoxvirus in Namibia and provides additional information on the presence of avipoxvirus in southern Africa.     

Effect of sucrose taken up by developing Avena fatua L. panicles on the dormancy and α-amylase synthesis of the seeds produced

Dormancy of seeds harvested from excised Avena fatua panicles grown in solutions containing sucrose increased with increasing concentrations of sucrose. Induction of this sucrose-imposed dormancy could be partially inhibited by the inclusion of GA_4/7 in the growing medium. The sucrose-grown seeds were fully viable and dormancy could be broken by methods commonly used to break dormancy, such as treatment with GA₃ or dehusking and pricking the caryopsis. Low concentrations of sucrose added to the incubation medium stimulated GA₃-induced α-amylase synthesis in mature de-embryonated A. fatua caryopses but higher concentrations inhibited it. The relevance of these findings to the explanation of the environmental component of A. fatua seed dormancy is discussed.     

The effect of nitrogen fertilizers on the germination and seedling emergence of wild oat (A. fatua L.) seed in different soil types

Ammonium-containing fertilizers such as granular limestone ammonium nitrate (LAN) and liquid ammonium nitrate (AN) proved to be most effective in stimulating germination and emergence of wild oat in sandy and loamy soil. In pot experiments, rates as low as 25 kg N ha^?1, significantly increased seedling emergence of wild oat. In sandy soil percentage emergence increased with increasing levels of LAN-fertilizer up to 125 kg N ha^?1 which gave 76·1 % emergence after 60 days. In control pots where no nitrogen was applied, only 21·6% of seeds planted emerged after 60 days, In loamy soil, as for AN in both soil types, high levels of LAN initially delayed seedling emergence. This negative effect disappeared approximately 15 days after seeding, resulting in no significant difference in emergence of wild oat where 25 to 125 kg N ha^?1 was applied as LAN or AN. All these rates, however, increased seedling emergence between 25 and 35% compared to the no-nitrogen treatments. Since the same rate of ammonia gas is not equally effective in breaking dormancy of semi- and deeply dormant wild oat seed, results of these experiments are not necessarily applicable to wild oat seeds differing in dormancy status.     

Breaking dormancy of Avena fatua L. seed by treatment with ammonia

Wild oat (Avena fatua L.) seed dormancy was broken by treating the air-dry seed with ammonia. Loss of dormancy was proportional to the concentration and/or time of exposure to the gas. The dormancy of several other grass weed species was also broken by ammonia but the gas had no effect on the dormancy of dicotyledonous weed seeds. The dormancy-breaking effect of ammonia was irrevocable and treated seeds could be stored for months without any decrease in germination. Germination of seed treated with sub-optimal concentrations of ammonia increased with after-ripening. Ammonia caused an increase in leakage of electrolytes from treated seeds, indicating an increase in permeability of the seed coat. The increase in permeability cannot, however, explain the loss of dormancy in deeply dormant wild oat where dormancy resides in the embryo. Des traitements à l'ammoniaque pour lever la dormance de graines de Avena fatua L. La dormance de graines de la folle avoine (Avena fatua L.) a pu être levée en traitant à l'ammoniaque les graines séchées à l'air. La perte de dormance s'est révélée fonction de la concentration et/ou du temps d'exposition au gaz. La dormance de plusieurs autres graminées a pu être levée par l'ammoniaque mais le gaz n'a pas eu d'effet sur les graines d'adventices dicotylédonées. L'effet de l'ammoniaque en levant la dormance était irréversible; le stockage des graines traitées pendant plusieurs mois n'a amené aucune diminution de la germination. La germination de graines traitées avec des concentrations d'ammoniaque sous-optimales a augmenté suite à une maturation après la récolte. L'ammoniaque a amené une fuite d'électrolytes plus importante chez les graines traitées, ce qui indique une plus grande perméabilité du tégument. La plus forte perméabilité, cependant, n'explique pas la perte de dormance chez des folles avoines profondément dormantes, car chez cette espèce la dormance réside dans l'embryon. Abbruch der Ruheperiode von Avena fatua L.-Samen durch Behandlung mit Ammoniak Die Behandlung lufttrockener Samen von Avena fatua L. mit Ammoniak führte zu einem Abbruch ihrer Ruhezeit. Der Verlust der Ruheperiode war proportional zu Konzentration und/oder Expositionszeit. Ammoniak brach ebenfalls die Samenruhe verschiedener anderer Ungrasarten, zeigte aber keine Wirkung bei zweikeimblättrigen Unkräutern. Die Beendigung der Samenruhe durch Ammoniak war unwiderruflich und behandelte Samen konnten während Monaten ohne Abnahme ihrer Keimfähigkeit gelagert werden. Mit zunehmender Dauer einer Nachreifung nahm die Keimung der Samen zu, die mit unteroptimalen Konzentrationen von Ammoniak behandelt worden waren. Ammoniak verursachte ein verstärktes Austreten von Elektrolyten aus den Samen, was auf eine erhöhte Permeabilität der Samenschale hinweist. Dieser Permeabilitätsanstieg kann jedoch den Verlust der Samenruhe bei Wildhafer nicht erklären, da die Ursache der Ruheperiode im Embryo zu suchen ist.     

Physiological basis of dormancy-breaking in wild oat (Arena fatua L.) seed by ammonia

The physiological basis of the dormancy-breaking properties of ammonia gas was investigated. Treatment of dormant, air-dry wild oat (Avena fatua, Montana 73) seed with ammonia did not influence the activity of the pentose phosphate pathway enzymes glucose-6-phosphate dehydro-genase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). Ammonia thus does not beak dormancy via increased activity of these enzymes. α-Amylase synthesis in de-embryonated endosperm halves which had been treated with ammonia and subsequently washed under tap water for 48 h increased five-fold. Catalase activity was inhibited by treatment of seed with ammonia but peroxidase activity was stimulated. In the dormant Montana 73 seed both ammonia and GA₃-stimulated germination could be partially inhibited by salicylic hydroxamic acid (SHAM), but SHAM had no effect on the germination of semi-dormant Oxford seeds. Ammonia treatment led to an 81% increase in respiration in incubating seeds. This increase in respiration was also partially inhibited by SHAM. It is postulated that loss of dormancy induced by treatment with ammonia is associated with the induction of increased respiratory activity. There is, however, no conclusive evidence that this increased respiratory activity is via the alternative respiratory pathway. The stimulation of peroxidase activity may also play a role in the loss of dormancy. Les bases physiologiques de la levée de dormance chez les semenees de folles avoines par l'ammoniac Les bases physiologiques des propriétés d'agent de levée de dormance du gaz ammoniac ont étéétudiées. Le traitement de semence de folle avoine en dormance (Avenu fatua Montana 73) avec de l'ammoniac n'a pas eu d'influence sur les enzymes de la chaîne pentosc phosphate, les glucose 6 phosphate deshydrogénase (G6PDH) et 6 phos-phosluconate deshydrogénase (6 PGDH). L'ammoniac ne lève donc pas la dormance par l'augmentation de l'activité de ces enzymes. La synthèse de l'a amylase dans des demi-endo-spermes désembryonnés, traités à l'ammoniac puis lavés sous un robinet d'eau pendant 48 h, a été multipliée cinq. L'activité des cataiases a été inhibée par le traitement de semences à l'ammoniac tandis que celle des peroxydases a été sitmulée. Pour les semences Montana 73, stimulées par NH₃, et GA₃, la germination pourrait être partiellement inhibée par l'acide salicyl-hydroxa-mique (SHAM); en revanche le SHAM n'a pas eu d'effet su la germination des semences Oxford en semi-dormance. Le traitement à l'ammoniac a entraîné une augmentation de 81% de la respiration pour les semences en incubation. Cette augmentation de la respiraiton était également en partie inhibée par le SHAM. Il a été retenu le principe que la levée de dormance induite par le traitement à l'ammoniac était liée à l'induction de l'augmentation de l'activité respiratoire. Cependent. il n'y a pas de preuve décisive que cette activité respiratoire accrue passe par l'autre chaîne respiratoire. La stimulation de l'activité des peroxydases pourrait également jouer un rôle dans la levée de dormance. Physiologiche Ursachen fuür den Verlust der Samenruhe nach Behandlung mit Ammoniak bei Wildhafer (Avena fatua L.) In dieser Arbeit wurden die physiologischen Grundlagen für die, die Samenruhe abbrechende Wirkung von Ammoniakgas untersucht. Eine Behandlung ruhender, lufttrockener Samen von Wildhafer (Avena fatua, Montana 73) mit Ammoniak beeinflusste die Aktivität der den Pentosephosphat Zyklus regulierenden Enzyme Glukose-6-phosphat-Dehydrogenase (G6PDH) und 6-Phosphoglukonat-Dehydrogenase (6PGDH) nicht. Demnach bewirkt Ammoniak den Abbruch der Ruhezeit nicht über eine erhöhte Aktivität dieser Enzyme. In Endosperm-hälften, deren Embryonen entfernt worden waren, stieg die α-Amylasesynthese nach einer Ammoniakbehandlung und darauffolgender, 48 h dauernden Waschung mit Leitungswasser, um das 5-fache. Die Begasung der Samen mit Ammoniak hemmte die Katalasewirkuking, stimulierte hingegen die Peroxydaseaktivität. In ruhenden Samen von Montana 73 konnte die durch Ammoniak und GA₃ stimulierte Keimung teilweise durch Salicylhydroxamsäure (SHAM) gehemmt werden; SHAM hatte jedoch keine Wirkung auf halbdormante Oxford-Samen. In keimenden Samen führte die Ammoniakbehandlung zu einer 81%-eigen Steigerung der Atmung. Diese Atmungserhöhung wurde durch SHAM ebenfalls teilweise gehemmt. Es wird angenommen, dass der durch Ammoniak veranlasste Abbruch der Samenruhe mit der Einleitung einer erhöhten Respirationsaktivität verbunden ist. Es ist allerdings kein schlüssiger Beweis vorhanden, wonach die gesteigerte respiratonsehe Aktivität durch den alternativen respiratorisehen Zyklus verursacht wird. Beim Abbruch der Samenruhe mag eine verstärkte Peroxydaseaktivität ebenfalls eine Rolle spielen.